Rod
Depending on what materials you're working with you might find that Trend or C MT have suitable routing bits and drill that will fit straight into the collet on the spindle. Trend certainly do router bits and possibly drills for aluminium as well as plastics and composites.
The alternative would be to make collets to fit direct to the router shaft that will accept the shank sizes that you wish to use, or make some adaptor sleeves. Depending on what cutters you want it might be possible to get them with 1/4 shanks. Microdrills have 1/8 shanks I believe so one or two home made collets might be all that you need.
Trend do make and supply collet extensions but they use the bigger shaft diameter – normally 8mm upwards or they might even be 12mm and up.
Keith