On 15 Jul 2022, ACMEBBS said the following...
Same issue here in the US. One thing I've noticed on Amazon & other
stores is the lower end Banana Pi's are priced where the RPi's used to
be. Check with the sysop of Freeway BBS  in your neck of the woods. Seem to remember he was running the BBS on a Banana Pi. Could be
mistaken...but if true...this might be your best option at this time.
There are a not of other IoT devices out there.  If it runs Linux chances are you and do almost anything you need on it.  Pi does have that awesome forum and support but if your building something from the ground up anyway typically it won't matter.  
If people can get BBSes running on their phone in the background then they will run on anything.  PIMP BBS stands for Phone in my pocket.  
So if you really can't find one and have a 1/2 way decent phone there is that option too.  I believe he did a full write up about how to do it.
|23|04Dr|16|12Claw
|16|14Sysop |12Noverdu |14BBS |04(|14Noverdu.com|04)
|10Standard Ports for SSH/Telnet Web/
HTTP://|14Noverdu.com:808
|20|15fsxNet/MRC Chat/Registered Doors!/50Nodes/No Time Use! Stay On!|16|07
--- Mystic BBS v1.12 A47 2021/12/24 (Linux/64)
 * Origin: Noverdu BBS (21:1/210)