I can not find a dually rear 4.11 gear to save my life. What option or what is compatible with a 69 f350 rear dually axle swap.

 

What do you mean by compatible? Bolt-in? Only 67-72 F-350 Dana 70's have the correct spring pad width and axle length. You could go with other year F-350 dually axles, but will have change the spring pad widths, and or drive shaft length and u-joints. You can go up to 98 10.25 axles for wheel compatibility, but you cannot use 99+ Super Duty axles due to the 170mm lug spacing. Check the big truck/heavy equipment yards for better pickings as there would be a better selection of axles. Don't worry about gear ratio as it is more important to find a good axle first. The gears can be changed later.