Never had a problem getting mine from Bob Roberts; having said that NTE89 is what I was told was a solid cross. Hoping others will chime in on that. Good luck never too cheap those.
Wow Ken literally posted that answer under me. Kudos
2SD870 is a pretty UN-remarkable device and available almost anywhere. Almost ALL Japanese and Chinese semi manufacturers make them using the same part number. The number doesn't change between brands.
Now THIS is a valuable resource. I usually do this manually - eg I plug in a part number into NTE Quickcross, note the NTE part, then keep plugging in similar parts until I get a hit.