Silversides are a safe fish. Frozen packs are in most freezers at petsmart/petco. Like Grif said, they shouldn't be a staple. Live minnows are generally not good, because whether you get them from a pet store or a bait shop, the conditions they are kept in are pretty horrible and many of them will have parasites or diseases. It's just a waiting game until your frog picks up something nasty.
Also, rosy-reds and goldfish have the highest thiaminase content. They should never be fed.

I raise garters which are more sensitive to thiaminase than most reptiles, so I have a lot of info about it. I think individual animals have different sensitivities to it (probably why it's never been officially proven); some babies will develop symptoms after only a few feedings of thiaminase fish and some snakes can go years on that diet before problems start cropping up. Additionally, the majority of the cases I see are in ribbon snakes. That's a subspecies of garter that eats almost exclusively fish, so if they're eating the bad kind problems would be more likely to show up. There have been reports of thiaminase issues in many reptiles, and even mink and otter in an area of Europe where the diet consisted solely of high-thiaminase content fish (they lived the natural lifespan, but many showed neurological problems like tremors or poor balance before death).
I know none of that really had anything to do with pacs, but I figured it's relevant considering there's not a lot of concrete info on how pacs react to thiaminase. Or if there is I haven't seen it... I don't think pacs are as sensitive as garters, but IMO it's just not worth the risk.