No problem :)
I had an oversupply too - it was a bit of a nightmare at times, but I wonder if it's the body's way of compensating.
My bf health visitor had also never hear of a posterior tongue tie - I ended up hiring a lactation consultant for a cou[le of hours. It cost me more than I could really afford at the time, but it turned out to be money well spent. She gave me the referral I needed (NHS).
Keep pushing. I think what you really need to find out is where a normal tongue tie would be treated, and work backwards from there. There were only a couple of places near me that TTs were referred to, so I phoned them and found out what they needed from me to go ahead. I know the last thing you need with a new baby (especially when you have problems feeding) is to spend a lot of time and energy trying to sort this out, but when bf started working for me it was like a weight had been lifted from my shoulders. In the meantime, see if you can get some nipple cream (Lanisoh helped me) on prescription, and take paracetamol if it helps any. I expressed one feed a day to give me a bit of a break - I don't know if that is something that would work for you.
There are also a number of breastfeeding helplines/resources, including the breastfeeding network (0844 20 909 20 - 9.30am-9.30pm) and La Leche League (www.laleche.org.uk/ - phone and email support). I'm sure there are loads more, but these could get you started. They might be able to let you know what help there is in your area, as well as offer practical advice. I used the LLL helpform, and got some really helpful advice, as well as confirmation that I wasn't bonkers for thinking DS had a posterior TT.
There are also some bf support groups listed here, but if my experience was anything to go by it can be just as hit and miss as your GP/health visitor. Not everyone is experienced in diagnosing TT.
I found details of a NI lactation consultant here. I don't know if she's any good, or if she has experience of posterior tongue tie, but she is the only private NI lactation consultant I could find.
I really hope you get some help quickly, or that someone who has had a TT snipped in Northern Ireland comes along with some advice.
You've been working so hard to take care of your DS, just remember to take care of yourself too :)