As far as I know, it is the males going to find the females, and not the
other way around... But I could be mistaken.
It would be nice if you tried to find where the female lives.
If you do, try to convince owners to have her spayed.
If you don't find owners, and if she doesn't have a colar, You should try to
trap her and bring her to vet to have her spayed... keep her AT LEAST until
she is healed from surgery... (then find a family, yes? :)

There are too many stray cats... and no body takes care of them and what
happens is that before you know it, there are tons of cats in your
neighborhood mating with eachother making yet other homeless kitties....
Those eventually either die from diseases, from accidents, or are picked up
and put in shelters where most of them are put down because they have way
too many :(

Please, help reduce the number of homless cats.
Thank you
Mia

I would be concerned if he never lost that tom cat smell and still sprays.
It's possible he was cryptorchid and still has an undescended testical
floating somewhere in his abdomen where it's still producing hormones.  If
so, that's a pretty high risk of cancer, not to mention he still has some
undesirable tom cat traits left.  Check into the vet who did the surgery and
ask him if he found both testes. You can also extrude his penis and if it's
spined, he is still producing hormones.  If is smooth, he's been castrated
and is just incredibly stinky. I think there's also a blood test that can
tell if hormones are still being produced, but the only cat cryptorchid
experience I've had is from the vet I work with having to open them up and
find them during regular neutering surgery.

I'd be concerned about having kittens in your garden soon if you really
have females in season out there.  Do they have owners?  Have you asked
the neighbours who they belong to?  Would you be willing to try and help
those cats which are coming into your garden?