Good comeback! 😉
I suspect that if you could find a decent supply of 12mm bolts, you should be able to put together a 12mm version for something not dissimilar to the 10mm set-up, albeit that thios will be heavier to carry to site, require more drill capacity and runs the very slight risk of causing more damage to the surrounding rock.
Try these folks for the relevant bolts:
http://www.lawson-his.co.uk/scripts/products.php?cat=Through%20Bolts%20Steel - M12 x 120mm seems to be the puppy.
Excluding carriage you're looking at £3.52 per bolt/hanger assembly, which is a damn sight better than the £7 or £8 that Petzl ones will set you back.
There will, no doubt be cries that the bolts aren't PPE-rated, but then neither are the maillons you're using 😉
Hello again darkness, my old friend...