if your looking for new modern derailleur you best bet is a midlevel Shimano ATB. unless you want to troll through ebay for the afore mentioned Suntour ones.
PS I moved this out to the general C&V forum for you
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“One morning you wake up, the girl is gone, the bikes are gone, all that's left behind is a pair of old tires and a tube of tubular glue, all squeezed out"
Sugar "Kane" Kowalczyk