You want to sell Shoe, T-Shirt online, etc… You need to be able to control stock for Virtuemart simple attributes. “Custom stock for Virtuemart Attribute” plugin with help you. When the admin creates a product will be able to set all its different attributes: color, size , stock and price adjustment.
Each product will have a unique stock number. So, in the back-end, You need to be able to control the stock. In the front-end, if the user buys a specific size/colour of the product, automatically the stock of the product for that size/colour will be deduct.
Click here to see more info: https://www.ladadeal.com/joomla-extensions/custom-stock-for-virtuemart-attribute