I bought some Q5's on 16mm (round) bases from LCK Led store....they
ran around $9.25 ea. One thing to note - maybe I received a bad batch or maybe just hit the LED lottery on my DX purchased Q5 (star), but these Q5's are not as bright and they're more on the whitish scale vs. the warmer side for the DX Q5.
www.lck-led.com
Your other option is to get the star based Q5's and remove the LED/re-solder to a 16mm base. This is done pretty easily using a torch lighter (from below) to heat the base.
Good Luck with your mods. :twothumbs