Precision supply Bursons and probably everybody else and do most of what you would need and also supply ARP rod bolts, K&N Filters and Transmission kits and a whole host of parts for A10, A12, A12a A13 , A14 etc so worth bookmarking and the online search is 4 pages just for A14 and nicely they give you dimensions such as Valve Head Diameter, Stem Length and Diameter all of which allows you to figure out what else may fit if for instance a 0.5 MM oversize valve head means you don't have to replace valve seats due to recession or too many refaces over the years because a slightly bigger head valve moves the seat to an unworn part of the valve seat insert.

So much usefull information can be found on their site for any number of suppliers brands.

http://www.precisionintl.com/Default.aspx