I know in this day and age many are against self-rolled solutions, but you already have multiple platforms integrated into this system, and it seems that maybe it may take more to modify a CMS or other complete system to offer partial functionality, plus given that you desire to include the Google maps feature, you would either need to self-roll that or obtain a plug-in, which makes upgrades a complete nightmare, more so that what you are probably already experiencing.

If you did a self-roll solution, you would be able to tie directly into your existing systems, since you obviously have heavily modified them, you should be familiar enough with the code to tie into the places necessary. If you use an off-the-shelf solution, you then have the fun of learning that systems code, where it can tie out to the existing system and in the long run may save time creating your own.

Just my .02