Hello and welcome to the forum,
Sleepless of Hartlepool here, at least I can try and do something more useful that just browsing at this crazy time of a morning!
Ducati Ohmaha have a great online parts listing thats very easy to use here:
https://www.ducatiomaha.com/pages/ducati-oem-parts I've looked at the 2005 ST4s info (page 26) for the very last version and see that the tensioner and plain bearings have different numbers:
702.5.022.2A and 702.5.001.5A (they might actually be identical, its a 'Ducati thing'...
70250222A - BEARING - Regular price $37.19: with a price, usually means available.
Popular wisdom used to involve removing the bearing and taking it to a 'good' bearing stockist and getting an FAG or SKF similar or better spec bearing but for fairly critcal stuff like this - thats obviously your choice.
Speaking of which, for a good European Ducati source try here:
https://www.stein-dinse.biz/product_...ducts_id=54798 Good Luck.