I won a couple of bids for Goofy banks on eBay but they lacked the plug or stopper at the bottom to keep the coins from falling out. I did a search for 'Goofy bank stopper' but only found plugs for piggy banks. I found an inexpensive group of them in varying sizes from Amazon (among other sites that had them for sell). It was a good price. I bought them one day and received them the next day.
I was able to find the right size for the two banks that I recently won the bid on. The package of plugs / stoppers came in a variety of sizes. I found ones that fit the banks. Now I can use them to put coins into.
search results for 'Goofy bank stopper' using DuckDuckGo.