As first installed, krita has a few stamp brush presets. Just type ‘stamp’ in the search box at the bottom of the Brush Presets docker to see them.
You can make your own stamp images as .png files, maybe 128 x 128 px or 256 x 256 px and import them in the brush editor to use as brushtips in the Predefines section of brushtips.
There is another collection available here:
Mojo Moo for comics
On the linked Github account, clcik on Download then click on the link to the mojo-moo-ink bundle, which has quite a few stamps in it.
Bundles can be imported with Settings → Manage Resource Libraries → Import.
There are some more stamps here:
IForce73's - Flower Stamps NOW AS KRITA 5 BUNDLE by Michelist
You can have any and as many stamp brushes as you like 