Yes, such a wallet exists, though it is still in beta: AtomicDEX (desktop version only) supports Namecoin (NMC).
You can even use the built-in “atomic swap” feature to trade your NMC, for example, for Komodo (KMD), which you can hold in the wallet and collect rewards or sell on many popular exchanges like Binance (affiliate link). Make sure you read the instructions first (found under Support). The atomic swap protocol requires that the maker and taker stay online and monitor the blockchains involved.
Exchanges which accept Namecoin can be found here.