Do a search here on the forum, the topic has been discussed before and several sources were mentioned. Or go to 3M's website, you may be able to purchase direct or learn the name of a local distributor of 3M products. Check your business yellow pages for automotive paint and finish distributors, the finer grades of Scotchbrite pads are used in auto paint work.
The Grey are available at home depot in the area were they sell stains & laquer finishes..
The White are in the cleaning isle & used for cleaning stainless steel
The white give the best factory looking finish IMO, I also used the white cut in 3"- 4" X 1" strips to apply the Mothers Polish on it's first coat over the frame before switching to an old white T Shirt..
Also alot of Bodyshop supply places "Used" to have the Scotch Brite pads in various grits as it's used to scuff primer/sealer before painting..
'Constantines' has them in any of the grits for $4.50 per 5 pk. Abrasive Pads - A69
They also have Micro-Mesh abrasive. Expensive per pad but it really works nicely. For a very high polish/shine w/o using a buffer and avoiding rounding corners,etc.
They start at 1500 grit and go up to 12,000 grit.
Considering most feel a 1200grit is a brilliant shine,,these are really something, but alot of labor to produce the results.
The last time I bought the white, maroon & grey 3M pads was at a small lumber&woodshop est.
Not a big structural lumber dealer but a smaller specialty type place w/alot of different types of wood and finishing matr'l. Catered to the hobby woodworker, carver,etc.
I think they were about 65cents/pad then if you bought 5 or more. That was a couple years ago.