And here is a link to an excellent tutorial that includes how to build various styles of bags, deconstructed from old antique versions http://al-leathercraft.silver.yp.com.hk/member/3389/diy/issue06small.pdf
I found the brass Gladstone style frames P-2867 on Ohio Hardware, and have requested that they become available on Hardware Elf. They are only 16" at this time - but it's a start