ExpressionEngine: How to conditionally hide modifier options depending on inventory count in Expresso Store 1.6+. {option_stock_level} can be used inside the {modifier_options} tag pair to output the current stock level for that modifier option. It can also be used (as in this example) to conditionally hide modifier options if out of stock.

EE: Store: Hide modifier option if out of stock

{modifier_options}
    {if option_stock_level > 0}
        <option value="{option_id}">
            {option_name} {if price_mod_val} ({price_mod}) {/if}
        </option>
    {/if}
{/modifier_options}