They're out there, a collection of 4" HB 10's shouldn't be too hard to assemble since even the 10-1's can be found on GB for $2-300. I'm trying to complete my entire M&P - Model 10 collection but as far as 4" HB's I have a -6,-8, and -14. I had a -10 but sold it, but those are common.

I prefer 4" Round Butt Heavy Barrel 10's and 64's and tend to wait for those, and I will usually pass on the SB's unless the price is really right. I even found a 5" RB M&P, and I really need an early 6.5" RB M&P.....those just look right!