Black Sheep wrote:
I've heard awesome things about Ring Lord and Mailletech, but if things don't work out there, check with your local SCA group. They will, doubtless, be able to point you towards any number of local and semi-local peeps who will be able to craft whatever you need.
Being one of the local peeps someone might go to in my area, I'll add that most of us order from Ring Lord for our supplies. Your mileage may vary, but it's frequently cheaper (including shipping!) to purchase cut rings from Ring Lord than to buy raw wire stock in any quantity locally. That doesn't stop people from manufacturing their own rings at higher cost for the experience
Point is, depending on the local prices in the metals market Ring Lord is probably your best bet for materials to make it yourself, and MailleTec for the welded stuff; they have crazy economies of scale working in their favor.
Edited to add:
As an alternative to metal sheets, you may check whether the local SCA chapter has a tailor/seamstress guild. There is a distinct possibility that they'd be helpful in the creation of a lower-cost sand-filled variant for you. Whether they would take it on as a commission or insist on making it a teaching moment for you so that you're not useless in the future will vary wildly between groups; expect that unless they think it's fun they may not be willing to do it even as a commission. Good luck!