2 wire ADT system.

Morning,

We have an ADT 2-wire fire system. We have a new out building that requires a sounder and flashing lighting to give warning that the fire alarm is going off.
ADT say that they no longer made parts for this system and the only alternative is to replace every sounder and call-box. This obviously is a lot of money.
Is there another way to do it, or to get hold of a sounder and flashing light for this system?

Thanks.