Ask IH: Can this type of software (SMS alerting) still be sold?

Hey guys,
twelve years ago my current (and soon former) employer had built a software for SMS alerting. This is used as an additional service so volunteer fire brigades, fire departments and hospitals can be alerted without using an expensive pager. A few years ago we added support for POCSAG/RPC1 to get fire alerts in realtime, without interfering with critical infrastructure.

Due to bad/no marketing, in the past we failed to expand our customer base. At the moment we have two large customers with around 5000 people as recipients in total. Because of different reasons I've overtaken the ownership of the product.

As a software developer I am unsure how I shall proceed now. The software itself is bulletproof. But I have no idea, how I can reach the market. Can this kind of software still be sold? Maybe even outside of Germany?
I'd highly appreciate any kind of thoughts!