Nordian are the cheapest in the UK if not there are a plethora of firms in the US who are very good. also if you know the exact engine model there is even Ebay ! The only other main firm in the UK that i know of is Belcher engineering......however i was quoted £50 + VAT for a single head gasket where as Nordian were quoting 75 quid (ish) for an entire gasket set including two head gaskets..... take from that what you will but i wont be going back there.. I heard (by rumour) that Belcher get their stock from Macs in the US.
Nordian have always responded to my emails bud.
also for info etc i recommend you buy this book....it is very good indeed
http://cgi.ebay.co.uk/Ford-Flathead-...ht_2545wt_1139
also the ford v8 1939 - 1946 forum is very good