I recently switched brokers. The guy I am working with now does not have his clearance. I have my clearance but not my CITES or my export license. So I need to pay $100 for my export license and apply for CITES then will be able to get more. I had been trying to get them through CA as a port of entry, but they are temporarily banned there (not sure why). I am trying, but it likely will not be until spring that I can get another big bunch of them.
As for assassin snails, I really prefer to put them in their own tanka nd then pick pest snails to feed them. By picking out all the adults and dropping them in, the egg clutches produced are reduced by alot. I prefer this method because the assassins do lay eggs and although the growth rate is slow for the young, its hard to completely get them out of a tank once introduced. Once your pest snails are gone, you would end up having ot supplement them either by reintroducing pest snails or feeding a meaty diet.
As an example of stocking (your mileage may vary), I added 4 to my 75g andhad no pest snails within a few months.
Keep in mind, if you feed a meaty diet (bloodworms, blackworms, etc etc) the snails will eat what is easiest and may not target the snails solely.
Another point to consider is that they willl often go after smaller snails first, so you may not initially notice a large change in your population other than new snails not being noticed.
Sorry for the wordy response, lol.