Repacement boiler for warm air system

[loose nut]

I have a central heating system with a boiler made by Johnson and Starley which produces warm air. It works very well and I do not want to change it for a wet system. However, it is now getting very old (over 40 years). I would like to change it for a new identical system. I have contacted Johnson and Starley who will not tell me how much a new boiler will be but on the telephone the person I spoke to thought it would be 'two or three thousand pounds, but less than a new wet system anyway'. This is a ridiculous amount for just a boiler and suggests that they will charge as much as they think they can get away with. Does anyone know please:

1. Are there any other companies which make warm air central heating boilers?
2. Will the current system continue to be safe to use if it is checked annually? I am concerned that the heat exchanger could fail leading to possible carbon monoxide escape into the warm air.