Hi bearminimum:
I wasn't familiar with numbered bands (we use coloured bands) but looked up Longman book bands here www.longmanbookproject.co.uk/fiction/lbpf01.htm and Level 8 is actually reading for typical Year 3 (England)/ P4 (Scotland) students - so ages 7/8.
So first off your DS is reading at the appropriate reading age (ideal being to having a reading level equivalent to your chronological age - so not quite 8 & successfully reading books designed for typical 7/8 year olds). So that actually looks good.
I suspect it's the reluctant reader bit that may actually be more of the problem. Several suggestions:
Does he like magazines? Comics? Sure they're not high literature or school books, but they have all sorts of reading to do and can encourage vocabularly. My DD1 (age 9) is a keen Dr Who fan. She's always after us to buy the magazines - we cave in once or twice a month. We thought it was totally useless until one day she said:
Mom, you'll never believe it. Mrs. X has changed our writing groups and I'm now sitting with my arch nemesis XXXXX
Trust me our DD1 would never have used such language pre Dr. Who magazine. There's a huge range of magazines out there for all interests - have a look, this may help.
----
We've also found with DD1, who was struggling with her reading (reading age roughly 1 year below chronological age and found reading out loud very difficult), that basically she found school books boring, so we've started incorporating our own as part of school reading (with school's blessing - although we actually didn't ask, they've been pleased with results and now widely encourage this approach).
Given your DS is reading more or less at the same level as my DD - can I recommend Lynne Reid Banks' excellent novel The Indian in the Cupboard - info here: www.lynnereidbanks.com/books/indian.html which we're currently reading. It's a total 'boy book' as my DD1 would say - but that doesn't stop her begging to read the next chapter - it really is a brilliant idea/ story. Some of the vocabularly can be tricky (Iroquoi - the name of the Indian tribe, etc..) so would highly recommend you read this with him and when he hits a difficult word, assure him that's a tricky word (or an American word) so he doesn't feel it's an issue that some words are difficult.
There are a number of websites that can help give you ideas for reading (as we've found school book selection is pretty dreadful, and our DDs actually crave a story with a bit of plot & excitement).
List of Classic books for children by age: www.kidsreads.com/lists/classic-lists.asp
Booktrust bookfinder also very good: www.booktrust.org.uk/books-and-reading/children/
The Guardian also had a nice insert about building a children's library: www.guardian.co.uk/books/series/building-a-children-s-library
---
Several things we do to support reading.
We find school books pretty dire, so we limit reading school books to at least 2x a week, unless it is one that catches our DDs interest.
We are reading the Lemony Snicket Series to them out loud - we do bulk of reading, but are getting DD1 (age 9) to start to read a page or two (our usual ploy is to say we're a bit tired so can't manage to finish the chapter tonight - usually DD1 can't bear that so volunteers to read out loud to us). Info on Lemony Snicket here: www.unfortunateevents.com/ Wikipedia summarises review & criticisms also discussed below that: en.wikipedia.org/wiki/A_Series_of_Unfortunate_Events#Reviews. Lemony Snicket isn't everybody's cup of tea - it's very dark - it's definitely not sentimental - but it's adventurous, the fact that children outsmart adults and always work out the problem first is a huge attraction & most chapters end on a cliffhanger - so it's very exciting reading.
Try and let your DS read something he choses and get the school to agree that he can write about what other things he's reading in the reading diary (if your school uses this). Our school has a clever ploy of asking children to recommend books for other children - this ends up with them discussing the book in great detail with the teachers, all of which benefits literacy. You could also suggest a library recommendation form is created for children so they can fill information in: Title, author, illustrator, publisher. Brief Summary. What you liked about the book. How you rate the book out of 5 stars. That kind of thing. Aside from creating the form (which an older year could design frankly) it involves the school in very little effort and means that the library is getting suggestions for new books.
Finally don't rule out your own childhood favourites.