my research shows that although shimano makes 18 and 20 tooth hyperglide (the kind you need, i think) cogs. it may be difficult to find them as single cogs. you may have difficulty too disassembling the sram cassette. sorry i have never even seen one. and i know cassettes can be engineered in many different ways.

but if i was to absolutely need to have it i would buy a couple of appropriate hyperglide cassettes that included the appropriate cogs and spacers, disassemble them and put them back together. this can be done. but it may be over your budget.

so it's a qualified yes to your question.