How should I file my penalty of cashing out my 401k early from my previous employer?

You will receive a 1099-R from the company administering the 401 (k).  Enter the1099-R exactly as you received it, and the penalty will automatically be computed for you.

Can I contact my old employer for that form?

It should be sent automatically to you by the administrator of the 401 (k) plan.  If you have moved in the interim, you might want to contact the administrator so that they send the 1099-R to the correct address. You should receive the 1099-R by the middle of next month, if not sooner.

Can I have them take out the taxes and pay any outstanding loans out before they issue the check?