Update 10/19/19: Finally got around to uploaded my modified H-bar ends with the idlers shifted to bring the belts back into parallel.
This is a custom X-carriage I designed to use a Titan Aero extruder+hotend on my D-bot. I used Draftsight to design the front and rear plates and had them laser cut out of 1/8"(3mm) aluminum. I machined the top and bottom out of 1.5"(38mm), 1/8"-wall, aluminum square tubing. Where the top carriage mounts to the bearing block, I milled two of the holes into 5mm slots so that it will bolt up to either an MGN12H or MGN12C (why doesn't everyone do this?). The holes that the front and back plates mount to are tapped for M5.
Originally, I was planning on looping the belts through the slots in the plates and using a zip tie to hold them. I edited the motor mounts to have slots to tension the belts. Unfortunately, I failed to plan ahead and doing so would have put my belts far out of parallel. I have designed a temporary solution that works but I'm not ready to share those files yet. I still think the slotted motor mounts are a good idea.
EDIT 11/08/18: As you can see, I used linear rails instead of v-wheels. I keep forgetting linear rails aren't "standard" for a D-Bot.
EDIT 11/14/18: Added a picture of my X-car with everything installed. Also removed the slotted motor mounts. They are here.
There are online laser cutting services but every quote I've gotten from them has been about ten times what my local laser cutting service charges. You can use the same company as me or google your zip code + laser cutter and find someone local.