There's a vendor on ebay selling some Lionel dummy couplers. They're not cheap but probably no worse that if you bought one from Lionel and they charged their flat rate shipping.
https://www.ebay.com/itm/LIONE...a:g:rFkAAOSwaktebzjY
Brassuers Electric trains also shows these couplers available on their website as well. I'm not sure if the current virus situation has closed them. Their parts depth is great, give them a ring.