Discovering True Muonium in $K_L\rightarrow (\mu^+\mu^-) \gamma$

Theoretical and phenomenological predictions of $\mathcal{BR}(K_L\rightarrow (\mu^+\mu^-) \gamma)\sim7\times10^{-13}$ are presented for different model form factors $F_{K_L\gamma\gamma^*}(Q^2)$. These rates are comparable to existing and near-term rare $K_L$ decay searches at J-PARC and CERN, indicating a discovery of true muonium is possible. The model uncertainties are sufficiently small that detection of true muonium could discriminate between the form factor models. Further discussion of potential backgrounds is made.