Hey I was wondering if anyone knew where I could purchase some 5 on 5.5" to 8 on 6.5" wheel adapters? I would like to purchase something of a pretty nice quality, not some backyard built stuff. And if you have any idea how much approximately are they?  

If you're really serious about beefiness, I'd upgrade your axles and get dedicated 8-lug hubs. Chances are if you're wanting to run 8-lug wheels on an axle originally meant for 5-lugs, you should upgrade the rest of the drivetrain.