You can simply remove any purchase buttons (cart or Buy Now) you have posted to your site for the product, and delete the product Details from your E-junkie Shop, then it would be impossible for anyone to purchase that product anymore.
Although deleted products do not appear in the Products menu of your View/Download Transaction Log screen, the product info remains in the log itself. You could e.g. select the date range when all sales of that product would have been made before you deleted it and View Log for that range, then click Download Log to save that log view to a file on your computer. Unzip the file and open it in a spreadsheet program like Excel or (free) Gnumeric, sort rows by the Item Number column, delete any rows that aren't for the product you want, and save the file to keep a permanent record of just that product's sales.
I have asked Development to weigh in here on whether you can un-delete the product or maybe create a new product to revive it for future-reference purposes.
