You can try Yahoo Japan, or eBay. Do a search 'cos some companies (mainly USA) sell replica ones.
However, be aware that the RA23/28 had adjustable fender mirrors (the driver side - not sure about the passenger side) by using a toggle thingo. To comply with ADRs your vehicle must have an adjustable mirrors (at least on the driver side), or, maybe it would be illegal on your car anyway seeing the RA23/28 came out long after this particular ADR rule in 1973. This ADR rule (I forget its number) specified that fender mirrors and such stuff are not legal on cars.
You can always try Toyota Japan to see if they have any NOS originalfender mirrors for your car. However, you'll have to check the relevant ADRs to determine if they're legal.