May be simplest to get them from the vet this time around, if you've not put them in before ask someone to show you, if you read the instructions and follow to the letter you will shove one or two through the cervix so careful how you go, especially on first timers, better they fall out than in. Getting them out of the cervix in one piece is a knack that you don't want to have to master!
Mole Valley etc etc do them but probably not worth the price difference unless you are doing a lot