Found a 5 pack of PIR sensors on Amazon for dirt cheap. Looks like they come from China so shipping takes about a month though.
I have used dx.com for a more direct service for several years 99.99% reliable.
They have a good range of stuff and there are technical links and user discussion there too.
Just ordered! Good find.
For anyone that didn’t order or wants more they have the same thing at a little higher cost with prime shipping now
Normally use aliexpress for orders from China, worth a look