We found the best source for casings was from a butcher who made his own sausages. We were able to get fresh casings and found they were a lot better than the ones we bought mail order, as they were salted. They needed to be soaked and rinsed first and were more difficult to handle and still tasted salty after soaking. Unfortunately our butcher only had standard size casings so when we wanted to make salami we had to use salted ox bungs.
We also found that the domestic electric mincer we had wasn't up to the job and couldn't justify a commercial one, so we bought a old fashioned metal hand mincer that clamps to the table and that worked really well (made your arm ache after a while).
I see you have already frozen your meat. We minced and made sausages that could then be frozen, as it would concern me to use meat that has previously been frozen, unless of course you were making small batches to use straight away rather than wanting to e-freeze the meat.