MDJ I picked up an extended magazine for my T3 30-06 from Cheaper Than Dirt for around $30. I believe it was sized for various .30 LA calibers (not recalling which at the moment) so you should be good. I will say I would have rather got another standard mag as I often field carry with one hand on the magazine and the extended makes this impossible. I just use the extended mag when I'm carrying my rifle on my pack and switch to the standard if I'm doing more than a bit of field carry.
We salute you, tender creature, for the sacrifice of your juicy meat.