Hi
Welcome to the forum, probably the best place around, certainly for getting Beta info in UK.
Your parts sources are in no particular order, Betaboyz, folk on the forum and Ebay (here and in EU). Watchout on Ebay for folk who do not really know what they are selling and avoid if poss any Chinese items such as bearings (several poor experiences have been reported). You can also look abroad on leboncoin.fr and there is an Italian one which escapes me at this moment as well.
As to info, get a copy of the Haynes book, usually around £5 on Ebay, but bear in mind mainly good for early cars, so you have to read between the lines of later ones. it is known on here as the Haynes book of lies to some, but I find it useful sometimes....
There are the parts books out there, in paper version expensive, but you can order a CD scan from here
http://www.viva-lancia.com/specials/cd/beta-cd.phpNot sure which version that covers on the S2, you may wish to ask if it was the pre facelift or facelift version the books cover.
I think for your car you should not have too many issues getting parts, the f/l one is far more common, but the 1600 is not so common in the UK.
We do of course require pictures of the car......!!
All the best
Peter