We describe techniques for adapting liquid-phase epitaxy (LPE) to produce thick ( > 100 mum) epilayers ("virtual substrates") of III-V antimonide ternary and quaternary alloys including InAsSb, InGaSb, InAsSbP, InGaAsSb, and AlGaAsSb. Multiple LPE regrowths are a straightforward way to achieve alloy epilayers with thicknesses typical of wafers and with continuously-graded or step-graded composition profiles. This can provide substrates with optical transmission and lattice constants different than currently available with binary compound substrates. Further, there are good prospects for combining these techniques with epitaxial lateral overgrowth for defect reduction. In some cases, this approach may serve as an alternative to modified bulk crystal growth techniques currently under development for making ternary alloy substrate wafers.