What worked for me was installing Twitter to get notifications from @rpilocator. Adafruit restocks (IIRC) on Wednesday or Thursday afternoons and you have a couple minute window before they sell out. Be sure to have two-factor auth set up in your Adafruit account in advance, it's required for pi orders.

This prompted me to look on Ebay, where Pi 4 prices are mad (>£100!) but the previous generations seem to be more normal. Wonder if it's worth me digging up any 3s I have and selling them.

I wanted one for a thing some months ago, and the 4s were out of stock most places and silly prices where they were available. 3s were in a similar state. I had a 3 spare but wanted the extra spec (USB3 and a bit more CPU umpf). I ended up getting a 400 instead as they were readily available at the time. When the 4s become sensibly available I'll swap it out for one and the 400 will become a toy for other purposes.

EDIT: sweet Jesus. Just checked the current state on Amazon and the 400s are listed at £117 for just the base unit, more than the £91 I paid for the full kit (the only in-stock option at the time) six months ago, the 4Gb 4 is £173 (next day prime) or £155 (up to two week delivery), and the 8Gb is down for a whopping £290! (next day, no cheaper slower options). The only Pi3 showing as in-stock ATM is £100. Maybe I should hunt out my spare 3 and make some drinking money from it!

I've not checked other sources.

I sold my 3B for a price that honestly makes me feel a little guilty at the height of the shortage, but to be fair it was an auction and I only set the reserve to MSRP. At least it went to someone who presumably really needed it and it was just sitting on my shelf gathering dust after being used for a project.

in rwanda? read the schematic diagram then hack left and right