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ON Semiconductor discontinued the FST3253 in SOIC a few years ago. They're
no longer available from distributors, only eBay and Asian sources and
perhaps some non-US distributors.

The TI SN74CBT3253CD or CDR (that second C is important; the R at the end
means it's tape-and-reel) is a plug-compatible replacement for the FST3253.
The version without the second C, as in the link from WA1EDJ, implements
the chip select lines differently so it's not a suitable replacement.
Here's one you can order on Digi-Key:

It's also available from Mouser, and probably other distributors as well.