Would a 5.5mm x 2.5mm adapter work? Take a look at ebay listing #292809943305 and see if something like that might work. This was picked this one randomly, you can probably find a US seller with faster shipping times. There were also several of the type you have now that might be large enough for your wiring?
This was the search phrase I used - Male 5.0mm x 2.5mm DC Power Connector Jack Plug Adapter. Other variations might yield different results? Amazon also has assorted items like this. I haven't located a 5mm x 2.5mm one.