The issue with direct links to products by SKU is that AspDotNetStorefront does not enforce a unique value on SKUs (because a full SKU can be spread across products, variants, variant sizes, and variant colors...therefore although multiple products may have the exact same sku, once they are connected with their variants they ultimately may have different SKUs). If you know that all of your products will have unique skus and you aren't really concerned about searching on a full sku (SKU + variant SKU suffix + color sku modifiers + size sku modifiers) then you could accomplish this by modifying the showproduct.aspx page. You'll can link to showproduct.aspx?sku=1111, pull the product sku from the querstring
Code:
String pSKU = CommonLogic.QueryStringCanBeDangerousContent("sku");
and then if the sku exists use that to query the database instead of the product id (searches on product id by default), and then if the sku doesn't exist or is empty use the default behavior.
<a href="http://www.aspdotnetstorefront.com">Shopping Cart Software</a>