I have found a universal mount for putting a fire extinguisher on the front (passenger) seat that allows it to move with the seat, much like the very expensive ones available for 911's. The mount is sold by H3R performance:
H3R Performance
I had it installed by Tony Miller at Translog in York, PA:
Translog
The base price for the mount is $79.99, but H3R does not sell directly to consumers. They charge a $15 fee to their dealers for a minimum order fee (the minimum order is dollar-based, I think), so you might want to consolidate your order with others to avoid the fee (my dealer split it with me because I also purchased the extinguisher from him).
Note that some fabrication was required; Tony added the support plate to the seat bottom. If you have questions, feel free to contact Tony directly -- I didn't install it, so I'm probably not going to be much help.
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