This is probably the biggest downside of club tennis for me too. Finding someone at a similar level is one thing, finding someone who is actually reliable is another.

I’ve had better luck setting a fixed weekly slot with the same person.
Once it becomes part of both players’ routine, there seem to be fewer last-minute cancellations.

A lot of players only want to compete, which is fine, but it makes structured practice harder to organize.
Sometimes 45 minutes of cross-court rallying and specific drills is much more useful than another random match.
I think it helps to be very clear from the start that you’re looking for training, not just match play.

Have you tried creating a small WhatsApp group at your club?
We have one where people post their level, availability and whether they want drills, points or a match.
It works better than messaging people individually every time.