You don't have to have the catalog, but I don't believe they do online stuff. Or at least last time I checked, the online stuff was so combersome that it wasn't worth it.
Just checked again. They have a site, but it's not geared to sell stuff online (other than the catalog).
Err, then again...
http://www.e-gunparts.com/itemnumber.aspLazs, what is the serial number or whatever for the stock?