I have three answers,and I don't think you will like either!)sorry).
1.If you CAN find mothballs then grab them,as the EU had declared the naptholene in them to be illegal,so any stocks left in shops are worth (to you) buying.
2,Mothballs are not that good at keeping cats away.They only put out a localised scent,and unless you want to make the whole of your garden stink of mothballs they are not much use.We tried it with our cats,and they just avoided the immediate mothball area.
3.Now this IS the provocative answer!
Get a cat of your own,this will keep all cats away from your garden (it's territory)..t's precisely because NO cat has claimed your garden,that all the other cats regard it as fair game.I do appreciate you might not like cats as pets,or may not be able to have them,but it's an idea.
PS:~
If you can buy one of those kids water guns( like a giant water pistol) cats don't like that and will son come to equate your garden with getting wet,and not return.Of course you have to BE THERE to squirt them,but it IS effective(if time consuming).