Out of Stock Problem on eBay dropshipping

I've been dropshipping for about 4 years now, most of the time with very few problems.
But lately I've been getting a lot of out of stock items from my dropshipping source.

I don't use any automated software programs so after I list all my 200 items for sale,
it's impossible for me to know when my dropshipping source goes out of stock. When they go out of
stock, it usually means every other vendor goes out of stock, too (meaning the manufacturer must
be in production and nobody else has it in stock). So what ends up happening is a lot of people
start looking for the product because it's out of stock everywhere and then they find my ebay listing
and buys it. Then when I go to order it from my dropshipping source, they have it out of stock and
everywhere else, too so I'm stuck with either waiting a few days hoping it comes back in stock
and can proceed to place the order OR I have to contact my buyer and apologize and say it's
on back order and ask if they'd like to either wait a few more days or cancel the order and receive
a refund.

I've heard of some software that can automatically remove my ebay listing or make it out of stock if my dropshipping source suddenly has it out of stock too. But I don't know.