What engine is it exactly and any motor oil will mix fine especially if its in the same base oil range and i wouldn't be afraid. I'd try Quaker state euro 5w-40 at Walmart. 19 bucks for a 5qt although not HM and on the thinner side.
But why get a HM oil? oil burning, leaking, or just because it says to use it beyond x mileage.
I'd use a diesel oil like delvac, rotella t4, supertech, delo or the travelers brand at tractor supply if you can get it, great stuff. Around 10-13 for a gal jug for all if you want a more high mileage friendly oil.