Consider trying ethyl benzene or the xylene isomers.  it may be that a cosolvent would be needed too (Methanol and/or MTBE).  I suspect the mixed nature of the molecule (aromatic but polar) is limiting solubility.   Just to be sure, is this the hydroxide form you are dissolving or a salt?

2,5-Dichlorohydroquinone is soluble in acetic acid. So please try the acid, but before that I think it is worth trying to dissolve this compound in ethyl acetate.

Have you tried to acidify the solvent? Maybe that's the problem.