the 4 slot ones seems to always be in stock, I guess only a few motherboards support that set-up, the ones with 4-way SLI support like my X99 classified, so that's why it's the only one always in stock.
as for what bridge to use for Asus x99 Deluxe with slots 1 and 3 (if you're not counting the PCIe x4 as one of them) you'll need a 1 space bridge
basically just count the number of empty expansion slot brackets between cards, if the cards are right next to each other with no space between them, 0 slot, if one space/bracket then you need a 1 slot spacing bridge, and so forth. granted this is assuming you have the standard thickness GPUs, and not a triple slot one that some companies make.