You can find a lot of nice frame on ebay
https://www.ebay.com/sch/Miners/179171/i.html?_from=R40&_nkw=frame&_sop=15
But it all depands on what you want to get and what money you can pay for it, the quickest way is to find a  local "gold hand" person who will made such frame for you and then you will decide what exacly you want and how much money you can pay for him for this work( i made it this way, cause i wanted to be made good with solid and stable frame  to pick and move anytime i want)