Bingham used to make a 30 round steel magazine (that required an adapter for the 10/22). Pre-1990's manufacture.
They are rare, and the last one I saw sold went for about $150 (including the adapter.)
Tactical Inc. makes an aluminum 10/22 magazine (
the TI25). They go for about $70.
Another option would be to bubba your own. Take a 10 round factory mag and glue the lower portion of another magazine to it. Maybe even cut-off the top 1/4 of a Mini-14 steel magazine and use the lower section.