I haven't seen one that a sub can't squirm away from. I got mine on Amazon. Strap-on Forced PU Leather Waist Belt Harness Holder (wand or vibrator not included) https://www.amazon.com/dp/B074J3X6KL/ref=cm_sw_r_cp_apap_LtImuToIRd8mg It holds the wand pretty well. It works great when my sub is strapped to a door in a standing position. If she's on the bed, I've found that ankle and wrist cuffs are not sufficient. In that case, rope tying her legs (just below the knee) to the side of the bed, in addition to wrist and ankle straps, helps keep her secure and prevents her from closing her thighs (her natural reaction when she orgasms). Hope that helps.
You could get a harness for a hitachi wand. hitachi makes one and there’s a similar cheaper one on Amazon.
https://www.amazon.com/Strap-Leather-Harness-vibrator-included/dp/B074J3X6KL
https://smile.amazon.com/dp/B074J3X6KL/ref=cm_sw_r_cp_apa_glc_fabc_FM1X1MSHMW94N3WFX7BW?_encoding=UTF8&psc=1 this is the one I ordered. it's coming today
Also, picked this up, and the wife has liked it so far. https://www.amazon.com/gp/product/B074J3X6KL
A harness that holds a vibrator ( https://www.amazon.com/gp/product/B074J3X6KL) (such as a magic wand, Domi, or even a Shibari Mino Halo) works.
A Wearable vibrator such as the We-Vibe Moxie works as well.
Higher end, you can look at the Lush 2 or the Nora from Lovense.
It really depends on how much money/time you want to spend on the endeavor.
Good Luck!
This is similar to the one I have: https://www.amazon.com/Strap-Leather-Harness-vibrator-included/dp/B074J3X6KL
Or here's how to tie one with rope: https://www.theduchy.com/forced-orgasm-belt-prusik/
Wearing some kind of underwear to keep things in place is essential to make it work, though not as sexy.