Ikea is one of the few places that do long ready made curtains - I think Habitat may do them as well.
I have bought curtains from Ikea and added my own blackout linings, which transforms them into quite luxurious heavyweight curtains. If you are not into sewing, you can buy ready made linings which you attach to the back with curtain hooks.
I've also seen some people who have bought 2 different colours of Ikea velvet curtains, and sewn them together, back to back, so that you have double weight curtains, with different colours on the front & back, IYSWIM? It looked pretty good.
Alternatively, there are some websites if you google 'long ready made curtains' which do 108" readymade lengths, but I have found them to be massively expensive.
Finally, if you have someone who is pretty good with a sewing machine, you could buy ones with a 72" drop, and buy an extra pair, which you can cut up and add a faux hem at the bottom. We did this for our bedroom curtains, and it looks great, because it looks like you have a really deep hem, and so therefore quite luxurious - but I would recommend you get someone to do it professionally (I think we were charged £10 - 15 per curtain?), and it really depends on the fabric as well.