First, Welcome to "The Yard!"
Scrapyard knives are usually sold in "releases." They sell out so fast that Dan Busse (owner) can't keep a constant stock in his "store," so you've gotta be on the ball to get them!
What usually happens, is Dan will announce a new knife here on the forum - he'll have pictures and descriptions, etc. Sometime after that, he'll announce a 48 and a 24 hour notice, including the price, and release time (usually an hour window) of the next knife. The evening of the Release, Dan will usually shut down the website for "maintenance" and reopen it with the new knife available in the order section, or he will announce a "go" thread, at which time you'll place your order.
The Scrapper6 will be a knife that should be made again. The original Dumpster Mutt was a one time run - but has returned in a few other configurations - a satin finish LE model, a full height grind coated "urban mutt" model, etc.
The best thing to do would be for you to stick around the forum for a while, as I'm sure Dan has something in the works to release in the not so distant future.
I'm not too up to date on Swamp Rat knives - I only have one - but you'll almost always get word here at the Scrapyard Forum about Swamp Rat releases as well.
If you're in a hurry, you can always check out the Busse Family Exchange over at Bladeforums.com for private sales over there.
Again, welcome to the Yard - please feel free to ask as many questions as you have and participate in the banter. Lots of good people here.