Depending on your location or region, worldwide, your options may vary significantly.
However quality comes at a price, though used or repaired boards may be bought at
some 'saving' over new-old-stock, or new replacement first-class product.
Various places offer parts, some may not have inventory of what you need all the time.
The following links are to some of several mac-centric independent service providers
who offer repairs and parts for Apple portable computers...
http://www.powerbookmedic.com/parts/
http://www.wegenermedia.com/
Some of the same kind kinds of businesses also sell repaired computers with some
kind of guaranteed coverage on the whole unit; yet where you are located may make
some great deals less likely due to shipping or other logistical restraints.
At times, you may find a differently damaged computer and then combine two into one.
Then if you are technically able with sufficient skills, guides such as iFixit can help.
There also are some video guides online for free, that may or may not be helpful in a
logic board issue; such as those macsales.com has on their site.
In any event...
Good luck & happy computing! 🙂
