When I first got my 555x 14 inch saw. I didn't think to buy extra guide bearings.
Wasn't long I need some. NAPA had a couple and got some more in in one day. They were pricey.

After some research found skat board bearings on *bay.
Much cheaper and work as well or better.
Look for:  
608Z
6000Z

Mac, I went that route once and the bearings I received were oil filled, not grease filled. Didn't take long at the high rpm's for the oil to start coming out and they didn't last very long. Maybe I bought the wrong ones but no where did I see anything about bearings packed with grease.  I now get the bearings at my local auto parts for about $2.50 a piece..

The cheapest I've found at auto parts store is in the $ 13 range.
If you have any. More info, sent it if you don't mind.

I changed one out this morning thus the post.

Look around your area for an industrial supply house.Usually you can find bearing there a lot cheaper and industrial quality also.

I bought some bearings on the big auction site.

If I remember right , on the 14" I had, the stock bearings were open bearings. I put sealed bearings in which last longer. I also try to adjust where the bearing isn't turning when running but not cutting. You get a little dust in there and they run all the time.

Also dust in an open bearing kills.

I bought mine at a local machine shop who has em in stock for around $3 each

Yup, my bearings are sealed. I adjust them like Kenny does.