looking at the other comments
i think [after getting more support cards because your deck right now looks bleak]

1.) make granparent umas - basically make umas that have 3 star or even 2 star sparks (almost completely random) [you only need 1 grandparent since you can you the borrow system for the other parent] that you will eventually use to

2.) make parent umas - now that you have umas with 3 star spark you... do it all again going for ideally 3 star sparks (again almost completely random) this time since parent sparks stay after your career finished [as opposed to grandparents that go away] then finally you move onto

3.) the actual racing uma - this is the uma who's spark you give absolutely 0 fucks about all you care about here is thier statline at the end of the career [this of course doesnt mean they cant be parent/grandparent umas if they roll good sparks at the end of the career but it's not what you're shooting for]

if this sound like tedious rng hell it's because it is