Gateway creation service
Creating gateways is a very time consuming process. First you need to get a test account with the payment gateway company in question, then their documentation and if you're lucky it's in English. Then you need to thoroughly read the documentation to make sure you fully understand the hoops that their system makes you jump through, and finally create test and support the gateway.
I actually enjoy making gateways, I think it's fun to get two systems to talk to each other but because it takes so long to do I avoid it like the plague.
Fortunately, Rob Joyce of the famed iJoomla has popped up offering a new gateway creation service for Jomres (among other systems). If you're looking for a payment gateway for Jomres then I can highly recommend that you zoom over to www.osdcs.com and see if they can put together a gateway for you, if it doesn't exist already. At last count they have already put together 16 different gateways for Jomres.