“Supply” professor is rather UK terminology, whereas “substitute professor” is US speak, what you probably need judging by your residence country. We are speaking here about “bolsas de profesores sustitutos” (= bolsas de sustitución), i.e. professors who substitute a vacant chair for a limited period of time in situations where the regular professor is not available, for instance when they are on leave or for some other reason.

The term “bolsa” meaning here “bolsa de trabajo” normally refers in the academic world to job listings, so I would go for “substitute professor (job) listings” if your target country is the States.

This is a good description of the situation in the States, but the problem is that it does not refer to the university environment, therefore the text uses “teacher” instead of “professor”. I understand this might be also applicable to the university world, though:
https://www.teachercertificationdegrees.com/careers/substitu...
Substitute Teacher Career Guide
A substitute teacher is an on-call teacher who substitutes for a full-time teacher when they are ill, taking vacation or maternity leave, or will be absent for other reasons. Substitute teachers can often choose to work on a part-time basis or accept longer-term openings that become available. This guide provides further information on what substitute teachers do, how to become one, and substitute teacher salaries and job outlooks.


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Note added at 1 hr (2023-06-08 14:24:29 GMT)
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Found this reference, they use UK English, though. “Interino”, not your question, is translated here as “temporary”.
https://www.usc.gal/es/departamento/economia-aplicada/direct...
Categoría
Profesor/a: Profesor Interino/a sustitución reducción docencia
https://www.usc.gal/en/department/applied-economics/director...
Category
Professor: Temporary supply professor to reduce teaching hours