Since it looks like everyone has been busy to go do more research, I went out of my way to stop by the dealer today on the way to do some shopping.
Good news: the CX-30 mirror housings are the same as the CX-50. The supplier is Penstone Mexicana, subsidiary of Ishizaki Holdings Corporation. It has the same ECE type approval numbers, same OES part numbers on the housings.
This means, there is a very likelihood that importing EDM Mexican built CX-30 mirrors will fit!
So, on to the part numbers for the Mexican built LHD EDM CX-30 mirrors:
Left side (aspheric):
DGK9-69-1G7 (w/o BSM, unheated)
DGK9-69-1GY (w/BSM, unheated)
DGL2-69-1G7 (w/o BSM, heated)
DGL2-69-1GY (w/BSM, heated)
DGL4-69-1G7A (w/o BSM, heated, auto dimming)
DGL4-69-1GYA (w/BSM, heated, auto dimming)
Right side (regular convex, no warning label):
DGK9-69-1G1 (w/o BSM, unheated)
DGK9-69-1GX (w/BSM, unheated)
DGL2-69-1G1 (w/o BSM, heated)
DGL2-69-1GX (w/BSM, heated)
As for the getting an aspheric passenger side mirror, using a UKDM driver's side mirror, you will need to take a small risk. The Mexican plant only manufactures LHD cars. All of the UKDM CX-30s are Japanese made, just like some of the LHD ones sold in Europe. The Japanese built CX-30s use Ishizaki mirrors out of their Japanese factory, rather than their Mexican one (makes sense).
I did a Google image search between the Japanese Ishizaki mirrors and the Mexican Penstone (Ishizaki) mirrors, and it looks like the mounting sockets are at the same places:
Mexican made (DG2L-69-1GX):
View attachment 311854
Japanese made (DFR5-69-1G1):
View attachment 311855
Like I said, there's a small chance it won't fit because of socket size differences. Worst case scenario, heat up the plastic backing with the heat gun, then with a putty knife, scrape it off, then do the same with your stock one, then swap the backing plates over. I have high confidence there won't be problems, however, but you are still at your own risk!
So with that being said, UKDM CX-30 right side (driver's side) mirror:
DADH-69-1GX (w/BSM, unheated)
DADJ-69-1GX (w/BSM, heated)
DFT9-69-1GXA (w/BSM, heated, auto dimming)
As for where to get them: like I said before, look for a UK seller on ebay that happens to be a Mazda dealer. There are a couple, last time I bought EDM parts for my 3 a few years ago and they're still around. Hint: randomly look up an EDM accessory from Mazda UK's website, then search the part number on ebay. There should be a seller or two that lists them for sell and uses the ebay global shipping program for cheaper shipping. PM them with the part numbers you want, and ask them to list your parts privately on ebay so you can "buy it now", then go from there. Pretty easy.