dtmf phone encoder?

howdy all. simple project here. I'm not an expert, but I think I can do this. I have several old rotary phones in my home. I'm having problems finding a project for a small DTMF generator that I can hold up to the mouthpiece when using a rotary phone to call in to a menu-based message system. Something pref using like 9V. batt supply. Seems they should be all over the net, but most seem based on use with a PC or for RF. Just point me in the right direction. Thanks in advance.

Touchtone phones can be found for almost nothing.

The Ni-Cad battery on my wireless phone died and a new battery costs 4 times as much as a new phone that already has the new battery in it. So I bought a new wireless phone.

My home uses "rotary dial service" so that I don't pay the Touch-Tone rip-off fee each month. I dial the bank using rotary dial pulses with the push-buttons then switch over to Touch-tones and do my banking.