For several years, the Bloomington Drosophila Stock Center has worked with the Fourth Chromosome Resources Project to generate new stocks.

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

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

and listed here.

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.