Depends on if you are loading shorts, longs or long rifles.
Rossi
10-100 usd
@1979-1988
Try e-gunparts.com
10-150 USD or so
Lacking anymore information; 10-100 USD
No known sn data published.
Blue Book of Gun Values
Not sure what a "22 cap" pump is. The magazine capacity of a Remington pump rifle will depend on which MODEL, and whether you are loading 22 LR, 22 Long, or 22 Short. The Model 121A holds 20 Shorts, 15 longs, or 14 Long Rifle cartridges. A model 12 would hold 15, 12, or 10.
$300--$550, depending on exact model and condition
Rossi
No one that I know of.