It appears Jaycar do 2, one with a VAC output and one with a VDC.

Searching SSR on eBay and omitting VAC brought up some results, although finding a DC one (that actually is!) with a decent amp rating (80s +) is porving impossible let alone a good price.

This is the best I could do:
http://www.ebay.co.uk/itm/SSR-60DD-DC-t ... 20cd90f6c6

60a

And 80a at a premium:
http://www.ebay.co.uk/itm/Solid-State-R ... 230ffeaafb