My RV is the same - no side mounted anything next to the front seats...just a big empty space, so I have searched and searched and had no luck finding anything in the after-market that I like...but lots of places will custom build anything you want.
So, the other idea's I found are:
1. The RV mfgt's will sell you anything that is part of a current model line-up, so if you like the armrest set-up in a different Coachmen RV, or a Newmar or Thor RV for example, call or e-mail them about ordering factory parts. For me, they would not quote a price (don't sell direct to the public), but referred me to La Mesa RV as a retailer who could order what I wanted and sell it to me.
2. Use a portable 12Volt refer/heater like this:
12 Volt 7 Liter Cooler/Warmer with Cup Holders RPAT-788 - $47.11 :
Can be removed, so it's dual purpose for driving and camping..and even use it in the toad.
Best of luck