The CJ3 like our ERJ aircraft are fitted with TCAS 2. You cant just bang in another independant transponder as it interferes with the TCAS equipment. We too investigated this after a $200 000 plus installation into 1 of our aircraft. The only aircraft that can take a GTX33 type stand alone transponder are GA aircraft with out sophisticated full EFIS cockpits such as the CJ3 and ERJ
The current Airservices mandate ( 1090 Squitter out) does not even match the USA equipment, so the fact is that when we sell our fleet they may be have to be modded again! Thanks Airservices for forcing Australian operators into a upgrade years before the manufactures themselves have even come up with a economical solution. The reason? It saves Airservices billions in not having to upgrade ground based radar systems the same as the US.. Our aircraft are already fitted with Mode S 'Enhanced" which is fairly new and way ahead of just Mode C... No wonder we do it tough here