You can use Wiktionary: https://en.wiktionary.org/w/index.php?search=kroj%C4%85
Almost all infinitives end with -ć, yes. Some of them end with -c.
But I wouldn't risk thinking of it as 'putting ć at the end of a verb'. Although it's quite common that the 3rd person singular and the infinitive only differ by this ć, it's not common enough to treat it as a rule.
On czyta. -> czytać (works).
On pisze. -> piszeć (doesn't work, the right one is "pisać" and there is no form like "pisa").
I guess there are a bit more... although that's generally quite rare, true.
'krajać' is a habitual form that some verbs have. Its only translation can be Present Simple, so it doesn't work here. 'kroić' works well for both Present Simple and Present Continuous.
Frankly, most habitual verbs seem quite natural to me, but 'krajać'... I don't know if I would use it myself.