You can find parts on here, PbNation and eBay. Those 3 are probably your best best but they are sometimes hard to come by (depeneding on what your looking for) because they are getting older and older these days.
For an explanation of different parts look here. The "I-O Library" has many faqs and guides that could help you out.
http://www.impulse-owners.com/page/?id=4But if that kid wants $150 for a tapeworm you need to run as far away as possible. They cost like $10 bucks. Unless you are referring to an LPR which would cost max about $60 if its an NDZ. So I'm not sure what that kid is selling you but its sounds like he trying to pull a fast one on you.
the short white bolt is probably a NDZ bolt and no you do not need orings. Keep that and you'll be fine.
the WAS board does have eyes and it is very easy to install.
Post pics of everything when you can so we can help you out even more. Much easier to give advice when you can see the gun.
Glad you like the site!