I got some seed about ten years ago and managed to produce a small tree which lingered on doing very little in the UK (where at least it was 'humid'.) When we moved to France (Loire Valley) I dug it up and transplanted it here. It never did very much but survived until last winter when very cold weather killed it off.
A French gardening company sells grafted plants (but at around 80 euros I don't think I'll bother!) but thanks for the advice on the conditions it needs. I hadn't realised humidity was essential.
If I can ever get some more seeds from anywhere, I'll try again, planting close to the pond and giving some winter protection.
Too bad that one couldn't make it ! I suppose it was weather./ climate.
In case you go loking for seed, please refer to this information on starting pawpaw seeds http://www.pawpaw.kysu.edu/pawpaw/ppg.htm#Seed Propagation
Most important, I think, is it says the seed must be fresh and not dried out. That could really make your quest difficult.
Thanks for telling us about your pawpaw experience.