You’d be very hard pressed to get parts out of Simplex. The problem is they are set up for a corp structure, meaning they need to set up an account, get a quote and a PO, etc. to really get anything done in their system. Its not as easy as just taking a credit card and handing you some items. if you were a business it’d be a lot easier.
You’d have better luck with the EST dealer, but the main issue you’ll run into there is you’ll never get a programming dongle out of them so you’d have to rely on them to, at the very least, come out and program it. Once again, labor isn’t cheap! They’ll probably charge you a grand or more just to set the system up, and $500 every time you want to change it. Seems silly but that’s what they’d get at any other site, so they are going to charge you the same for your simple system.