For several years, the Bloomington Drosophila Stock Center has worked with the Fourth Chromosome Resource Project to generate new tools for the fourth chromosome.

New mutations in fourth chromosome genes are described in this recently published paper:

A new Drosophila melanogaster research resource: CRISPR-induced mutations for clonal analysis of fourth chromosome genes

You can find available stocks on this page.

We also have a new paper discussing a common problem with fourth chromosome crosses:

The underappreciated, underrecognized problem of fourth chromosome trisomy in Drosophila melanogaster stocks and a simple, general method for building diplo-4 stocks from triplo-4 stocks.