Hi Vincent,
Can you type in those two words?
(Sorry, just kidding )Basically, this type of request should be addressed to Outerra community, as currently they are making content for Outerra.
Personally I have Su-27 in development for Outerra, which flies already, but postponed due to high amount of work that's on me now.
Another way for you to get Mig-25, is to find a ready model and import it.
Using the sample script from Mig 29 and adjusting it's properties.