I've seen a few different kinds. First, there is atlas mikes pre-tied sacs that come in a jar. Never tried these but I'll believe slayer that you may as well use PB. I've also seen some on the internet and on ebay but never tried any of these. I think some bait shops sell salmon roe in the winter and you can tie them up yourself
I agree with Slayer. I have tried both and koke roe wins hands down. Fresh or thawed koke roe is an entirely different consistancy and smell than the kind you buy. That kind comes from your ocean going salmon. Different species than ours and our trout are looking for what is common to them. The purchased stuff tends to be really milky where the Koke roe is very oily. I was catching macks like crazy one year at Williams Fork on koke sacks until I made the mistake of combining my remaining koke roe with some that I had purchased from the bait shop. Gave it a completely different smell and apperance and my catching came to a halt.
I like to use eggs from whitefish myself. I also use rainbow or brown trout eggs too...never koke eggs, but I guess that's cuz I don't catch hardly any kokes. I like to get the eggs and mix it w/ borax rather than using netting.
A good thing to do is if whitefish are spawning in a shallow pool in a river, fish with eggsacks below them. The big browns and bows will hammer it.