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One place to look is the manufacturer's website. Either somewhere on their web page for the IC itself (maybe it has a section called design resources/resources/reference designs, etc.) or the section of their website that covers Spice models. Models seem a bit hit-and-miss IMO, often one you want to simulate is missing, no idea behind the reasons for manufacturer's making or not making Spice models.
It's possible that if it's a "mature" part (enough for
someone to have decided it was worth their effort)
there could be a LTSpice symbol & model on the
Yahoo! Groups LTSpice repository. That's fine if you're
using LTSpice; beware however that models using
LTSpice's mystery behavioral functions may not
play correctly in other simulators, depending on
those simulators' A and B source support and syntax.