Film first- most of the cost effective sources in the UK that offer a good range are mail/internet/telephone outlets not retailers in the true sense. These are more likely to have what you want in reasonable bulk and they can deliver quickly. Whilst the prices may be good in UK terms, they probably won't match the cheapest you can get in the US- though they will certainly be cheaper than I pay in the US if I run short and have to buy 120/220 locally. By way of example I'm currently paying about $4 per roll for TX 120 and more like $3 for Ilford.
Destinations. Well no doubt Glasgow and Edinburgh will occupy a few days of your time, but the real scotland lies north. On the assumption that you'll have a car, drive north from Glasgow for two hours and you'll be in Glencoe and if you just drive north from there keeping close to the west coast and following some of the little roads, you'll see the best Scotland has to offer at that time of year. If you get right to the top, around Durness and Tongue, so much the better. If you can get on a boat across to the Hebridean Island of Lewis and (especially) Harris then that's great too.
A couple of things you need to know. First its likely you'll find the midges out. If you know about mosquitoes there's possibly not a lot more you need to know about midges except that they're smaller but no less voracious.
Second, have a look at the sunrise/sunset tables to understand the length of day you'll be coping with in June. Given that as ever the best photography is likely to be late and early you'll find they aren't separated by much.