Good morning huffdaddy. If you ever find that you are out of cultures, the maltese and halloumi cheeses can be made with rennet only.
As for your setting problem, there could be a few reasons. One could be that you are adding too much rennet or that the rennet that you've added hasn't been stirred in well enough. Rennets come in different concentrations, so you need to check the instructions on the container and see what they advise to use, and not just add what the recipe might say.
If you have added the correct amount of rennet it then need to be diluted in cooled boiled water. A couple of tblsps is sufficient, then slowly poured over the milk, (which has been bought to the correct setting temp) while stirring continually for at least 1-3 mins. This ensures that the rennet is well mixed through for an even setting of the milk, otherwise only the areas where the rennet sits will set, causing an uneven set.
If you are finding that the milk temp keeps rising, immerse the milk pot into a bath of water while it is setting keeping an one on the temps though in case it goes too low. If the milk sets too long, or the temp is a little too hot, it can tend to separate the curd and whey early, leaving the curd to clump on the bottom with the whey separating out. Ideally, you want to cut the curd before that happens, so you may need to shorten your setting time if this is a regular occurance.
Hope this is of some help.