what are you looking for? honestly the best bang for the buick is a intercooled engine swap. you can usualy buy a whole engine, turbo, intercooler, harness and everything for like 1200$. then its all easy from there- finding hot air performance parts its a challenge
Poston buick sells some stuff for hotairs, like headers and up pipe. jaysgn.com also sells the up pipe with the flex joint in it. Not sure if you can get a downpipe anymore, ATR that made them went out of business, and I haven't heard anything about keith mease in a long time. Your best bet would be to look for a used ATR piece or if you are lucky a Lee Thompson piece, but fat chance on that one. You could also have a downpipe fabbed by a local shop that is worth their salt (where there's a will there's a way). You could also send your stock turbo to john craig at limit engineering for a hefty fee that will upgrade the internals to flow quite a bit more. Summit or jeg's sell the hooker cat back exhaust for a reasonable price as well. I would do exhaust mods first, they seem to net the biggest gain. Injectors and chip you can get anywhere, but you will want to swap to the 87 ecm first, which is easy and will allow your scan tool (which you do own, correct?!) to read way more data . That's all I can think of right now for bolt ons. After that you get into the motor.
There are guys on TurboBuick & T6P that say on a hot air Alky is one of the best and easiest mods. With a relatively stock car it can get the car into the 12's. I do not have Alky on my 84 but am just passing along what I have read.