OK, so you want to flash... well, here are the basics on how it's supposed to work
New options can be 'flash' loaded into a FlashPort radio. The physical requirements are a SmartRIB box, PC to SRIB cable (not always the same as the PC to RIB cable, you need a programming cable which has all the necessary pins connected properly and many aftermarket cables do not but the genuine Motorola article does), and a FlashKey, which is placed between the SRIB and the programming cable.
The FlashKey is a 'dongle' which carries a program of its own in it. It communicates with the SmartRIB. The last part of the system is the Flash upgrade software. It works with the RSS, and communicates with the SmartRIB and dongle to control the usage of the Flash file. A FlashKey can only be used for as many radio upgrades (and of the same type) as were purchased. The file on disk is not useful anymore once the key's allowed number of uses is up. The software file itself remains intact, but the key is rendered useless for any further upgrades.
Motorola is the only 'official' source of Flashport upgrades. They vary in price according to what options they add to a radio. SmartZone trunking supposedly runs about a thousand dollars per radio upgrade, while some other options like Modat may be only 100 or so.
Now, don't confuse flash upgrading with firmware upgrading. It really does depend on what kind of radio you are dealing with. You don't always need a SmartRIB to do a firmware upgrade. For example, if you're talking about PRO radios, the HT and CDM series, you need the re-flash adaptor,HLN9742, and a regular RIB and the Programming/Flash cable, or you can delete the RIB and just use the RIB-less programming cable. A SmartRIB is not necessary for this application. The software is downloaded from Motorola's dealer services website (you have to be a dealer to log in).
You may want to check out the Flash Code Decoder if you want to see what is included in a particular flash code. The interactive version is pretty cool too.
Note that these flash decoding tools may not be completely accurate, your mileage may vary.
Getting flash upgrades is nearly impossible unless you're an original buyer of the radio from Motorola directly. Officially, they don't sell any flash upgrades to any secondary market radios. Exceptions are rare.