Coming by anything from the Combat Digi-Q line is VERY hard. Production stopped back in '04, not to mention the product line was available via import from Japan ONLY so prices were high.
There's a knock-off brand called VsTank though and they have the R-type line with the rotating turrets (just like the Combat Digi-Q rotating turrets had) and these VsTank*R as they're called just started being released and so far it seems ToyEast is selling them along with accessories and spare parts!
http://www.vstank.com/rtype/index.html
and
http://www.toyeast.com/v3/catproduct...id=1528&clvl=4
You can find a set (2 Tanks) for ~$65 shipped from ebay:
http://cgi.ebay.com/VsTank-R-DX-COMB...QQcmdZViewItem
Good luck!