Hi Peter,
There is no native ATM module being supported for the ISR 4451 anymore. Then again, the majority of native ATM networks has been phased out almost two decades ago. Are you sure you need an ATM interface? Are you perhaps looking for a DSL module that internally still uses ATM?
Just for your information, this page documents all supported modules and interface types for ISR 4000 series routers:
https://www.cisco.com/c/en/us/products/routers/4000-series-integrated-services-routers-isr/relevant-interfaces-and-modules.html
Best regards,
Peter
