However, they do have 20-30k mattress money to put down on a house, and they typically finance the remainder through a private money source, 12-year @ 14.5%.

I personally use Private lenders.

My brother and I started a private equity real estate investing company, aptly named Beyer Brothers Holdings LLC, in the Phoenixville, PA suburb of Philadelphia.

My firm raises capital in the form of proprietary private equity for investments and structures joint ventures.We specialize in condo high rises and multi family townhouse developments etcIs this your area of expertise?

For education purposes, I want to know how is the "payment" calculated when it comes to having a private lender provide 100% purchase price of a deal for either (1) a 6 month term or (2)  1 year term if the repayment shall be in the form of monthly payments until the loan is due and its at a 8% rate?

You may be able to find private money sources in your area.

I do have a private lender/ silent partner presently that prefers quicker turnover, which leads me to fliping.  

After 25 years of investing and lending privately as well as doing JV deals I think I've seen most everything.

Are those funds from a private individual or is it a fund?

I have also gotten a family member to invest via a private loan to me because I show what I'm doing.