What options do bonnevilles have with suspension upgrades?

sway bar, springs, strut bar, handling kit etc.....

the upgrade is the GXP suspension. i Installed it on my car, it has the FE5 suspension code, stiffer springs/struts, and thicker sway bars.

I did a write up on the swap

where could I go about purchasing some of these parts....

Nice! Can I put that on my 99 SSE? Where do I find one and What'* the cheapest I could pick one up?

Check a local bone yard. Or if you want to pay an insane amount of money, you could go knock on Mr. Goodwrenches door.

I have been checking junk yards but GXP is a rare car to find

For a 92-99, you can go up to the ~96-99 SSEi suspension only. No 2000+, and absolutely no GXP parts without more mods. The 2000+ Bonnevilles use a different chassis. I think the SSE should have the best suspension. If you are having problems, you can go beyond stock upgrades and do coilovers and work with more suspension parts. 95naSTA put coilovers on his Bonneville, and he has a write-up about it on b-pro.

what eibach lowering springs?

I don't believe Eibach makes any lowering springs for a Bonneville. When you use lowering springs, you have to change the length and travel of your shocks or struts by changing them as well. It'* more than just getting shorter or weaker springs to drop your ride. To do it right, you are looking at some serious $$ and you don't want to do it wrong.

Check out some struts, decode the system that makes up their modeling numbers and such, and see which ones are shorter. Then see how much shorter they are and simply have some springs cut and re-welded to the appropriate length. That'* probably not the good way to do it, but it'* like replacing struts and springs.