from octopart FQA28N15 is still available and we can buy them with more peace of mind :Yes, they are becoming scarce. Newark still has stock available, and Ebay seller POLIDA is a source for genuine parts.
We will need to find alternate parts before long. The IXTQ36N30P is another part that I have in mind for the F6, and it has a likely P-channel match.
The chassis that I used for my F5m has reappeared on Ebay. For some reason it disappeared from my lists for a while.
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Aluminum Chassis DIY HiFi JC3
It is a little more expensive than I remember, but comes with a good kit of fasteners, AC inlet and power switch.Hopefully this isn't inappropriate, but I just received 100 FQ28N15 ONSEMI from Newark, 10 are spoken for and I will keep a couple dozen +/-. If anyone is interested, before shipping they are $1.90/ea plus shipping, let me know if interested in private conversation.