"NTE" used to be a big replacement-parts vendor with
a good interchange reference book. The old ham / TV
repair shop I used to hit had a peg-wall full of little zip
bags of transistors. I'd bet Digi-Key has killed that guy
off, if the chain smoking didn't.
You might find selection guides at major vendirs, still.
If you picked one with roughly-similar device types
(like, don't go to Semicoa looking for a 50GHz GaN
HEMT).
I turned Mr. Googlez loose on the simple P/N and the
first thing that comes up is multiple eBay vendors selling
onesy-twosey (though you may not like the price, it's
not like you need that many for a one-off project, right?).
If you're patient you can snag a good deal, maybe. Or
pay the "urgency tax".
You could of course drill into detailed attributes and
design care-abouts, and try selection guides with that
kind of search criteria.
The obsoleting of a Motorola part by Microsemi probably
is from them gutting one of their operations that used to
be in the "buy and hold inventory for someday" business.
Microsemi has been a "thatch rake" in the semiconductor
segment, buying up, breaking up, selling off pieces of
companies they've been buying up for decades (before
being themselves bought my Microchip, who cares not
for the trailing edge once its "contribution margin" falls
below threshold-of-caring.
You might look at outfits that are still in the "crusty parts
for high prices" segment, like Rochester, if eBay fails you.
RF-focused stocking distributors' applications engineering
might be convinced to help you out if you lie about the
quantity you'll be ordering and how soon.