This is my first post ! I myself made my first Electric Guitar "From Scratch" and I did a lot of research on suppliers in the USA. I purchased a Bookmatched Flamed Maple top from "Luthiers Mercantile" (
www.lmii.com) in California. The quality was AAA.
Great looking piece of Maple. I don't know if they ship to the UK but it might be worth a try. There is also another company that oddly enough carries Guitar Hardwood called "Grizzly Industrial" This is is an industrial tool company.
The ownerScott Balolia has a passion for building Acoustic Guitars so he started to carry items to build guitars. (
www.grizzly.com) They also carry great woodworking tools for a fair price & quality is good.
Also, sometimes you can find hardwood items on EBay (I would not buy it from there)
Good Luck !!