Add Tamiya TRF buggy shocks to the list - I was fortunate to get some here on Oople, but can be had on eBay for under £50.
Associated ones should be readily available for around £25 used (or
new for a
little bit more), best upgrade for those are the bleed caps at an extra £5 or £6.
As the biggest issue with the Madrat shocks are the tops popping off, you could try to find alloy shock bodies and alternative caps - not sure what will fit, though - perhaps changing pistons to match the shock body would be enough?