You can order the parts right from IBM. They have a toll-free number for service parts on their web site. I've ordered ThinkPad parts from them within the past 2 months, they were friendly to deal with. Don't know about ordering through a dealer. They would probably want to install the parts, too.
However - you will be miles ahead of the game if you know the FRU number for the part you need. You can get that from the maintenance manual. The people who take the phone orders know nothing about tech support, so you have to be sure what you order is what you need. They can help you a little bit with looking up numbers from a list but you are mostly on your own. Some of the parts are listed on their web site, but if it's not there don't assume they don't have it.
Prices for some of the service parts can be unreal. Their shipping is also pretty expensive, because they only do 1- or 2-day air. For example, I needed a rear panel for a 4 year old ThinkPad. They had it in stock for like $12, but shipping was about $14 - so $28 for a 1-inch by 8-inch piece of plastic, they sent it in a huge box, pretty funny. But what else are you gonna do?
Good luck, let me know what you decide to do.