A couple of things to try. One, be sure you're using the BlackBerry Browser, not Opera Mini, and that your emulation is set to BlackBerry. Using anything else can fool Google into downloading the wrong version, or refusing to download at all.
Assuming you've got the browser set and it's still not downloading, try going to "http://www.Google.com/m/" from the browser. Then select More and download the maps from that area. That's what I did to get version 2.2.3 on my 8830.
Try doing and OTA install. Here is the link: Google Maps. It is the latest version. For some reason there have been issues installing with the application loader on the BB 8310. Good Luck!
