GUNPARTSCORP.com and JACKFIRSTGUN.com carry lots of parts.
Try e-gunparts.com
20-50 USD
10-100
10-100
Best left to a gunsmith
10-30 usd
Gun Parts Corporation (AKA Numrich) is the source for replacement parts for most obsolete firearms http://www.e-gunparts.com/productschem.asp?chrMasterModel=1980z66 they list all the standard Model 66 barrel lengths
this rifle should be marked .22S,.22L,and .22LR.
20-100 or so
Sometime between the mid 1950s and 1968.
About $150 if its in GREAT condition and has both the cylinders .22 and .22 magnum.