I take it from the names you're mentioning that you're in the States somewhere, so my knowledge of suppliers in the UK won't help you much. What you need to look for is either a local complany of reasonable size that does alarms and access control and which wioll also sell you the parts, a good electrical wholesaler or a national electronic components distributor (in the UK we have RS, Farnell etc). Your basic plan is good; you just need a reliable and helpful distributor
I found my local suppliers these security companies have the annoying habbit of trying to sell you on things you do not need or try to get you to have them install it. One guy tried for a hour to get him to install a lock when all I was trying to do was buy the lock. After looking at the options I think I will go with an online supplier for the locking controls.
TS-18 Alarm Control (request to enter)
Altronix TP2420 Plug-In Transformer (power)
von duprin strike lock (lock)
IEI International Electronics 212I FLUSHMOUNT INDOOR KEYPAD (keypad)
Safety Technology SL2107 SL-2107 (request to exit)