The only way is to catch one in a previous game and transport it into US/UM. You can get Persian in ORAS at Mirage Forest by Route 124, transfer it using Pokemon Bank, and breed it in Alola for it's Kantonian form (see below). You could also catch Meowth in Diamond/Pearl/Platinum at the Trophy Garden or in Soul Silver at Routes 5, 6, 7, 8, 38, and 39 -- then go to the Poke Transfer Lab at Route 15 in Black/Black 2/White/White 2 -- then use the Poke Transporter to send it to Pokemon Bank -- then put it from the bank into your USUM game.
If you take any Alolan Pokemon and evolve it in Ultra Space, it will turn into it's non-Alolan form. Beware though, evolving any Pokemon with a regional variant in Alola will evolve them into their Alolan form. In other words, if you take a Kantonian Meowth from ORAS and transfer it to USUM then evolve it, it will turn into Alolan Persian.
You can also breed non-Alolan forms by having the non-Alolan Pokemon hold an Everstone. So if you put a Kantonian Persian in the Nursery while holding an Everstone, the offspring will be a Kantonian Meowth. If you want to evolve that Meowth into Kantonian Persian, however, you'll need to evolve it in Ultra Space.
Hope I helped!