Originally Posted by rccardr

Least expensive way to do this is to buy a Shimano/SRAM 7 speed HG cassette, take it apart, file down the one narrow slot to the same size as the others, then use 6 of the 7 cogs and spacers. To hold it on the freehub, you'll have to slightly reduce the thickness of the built-in spacer on your existing DA small cog, which must be used because it has a smaller thread diameter than non-DA small cogs. A Dremel tool works well for all of that work, but it can also be done, if somewhat laboriously, with a good hand file, acompanied by a few beers.

More expensive is to source a UG 7 speed cassette with the cogs you want, do the same deal on the small cog, etc. They are out there but getting harder to find in specific sizes.

Certainly lacing up a newer 8-9-10 speed hub to your existing rim and spokes will also work, but having just done what you're contemplating I felt using the original hub was somewhat more elegant.