Greenfire Farms doesn't list anything they're not currently selling or have given up on. For example their Marans were pulled out by Bev Davis for the year, and their Tolbunt Polish I'm assuming they gave up on.
I mention Silver Laced a lot because the difference in it and spangled is just one extra gene - the laced one. Otherwise, spangling is melanizer, lacing is melanizer + lacing.
I mention using Silver Ameraucanas and possibly Wheatens instead of others because White is often just black with white masking over it. Once you get rid of the white, you have black, which of course you can't make spangling from.
Same with blue, you just get a blue bird with black spangling. Silver (duckwing) is good because it already gives the silver colored base and is very easy to "mold" when crossing silver laced into. You already get a pretty laced looking bird on the first go, then working into the next generations gets rid of the red from the Duckwing and also works down to spangling and not lacing.
Wheaten I'm only assuming is another good one because it is pretty similar to Duckwing, and also Wheaten Ameraucanas are in general far more common and larger, however they won't make as good of crosses as Silvers when it comes to trying to obtain the silver spangled look.
Spitzhaubens are good, about as good as Polish. They have the V comb, the spangled look, but usually a thin, small body. Also, the spangling may dissipate if bred wrong.
Like I said, either way, there's good and bad to 'em all. But they will all take a while to reach your V-combed, EE-looking blue/green egg laying silver spangled bird of large size.