If you want nice stuff on a probe with an analog center freq of 10MHz, you can do PWM (in various forms) with an higher freq. Now 10MHz is not be the lowest probe freq avail, it depends on the usage. Higher freq gives better resolution, but has a worse penetration.
A 10MHz transducer will be resonant at 10MHz. If you drive it with a square wave at 10MHz, it will naturally respond best at frequencies that are 10MHz, and will very poorly respond to frequencies that are not 10MHz. Thus, a 10MHz square wave driving a 10MHz transducer will produce a pretty good 10MHz sine wave sound signal. This does depend on how sharp the resonance is of the transducer, but it shouldn't be that hard.
Ignoring that, creating a 10MHz RF sine wave isn't that hard using classical analog techniques: wifi chips in modern computers create a 5MHz carrier wave that can be amplified and doubled with some cheap off the shelf parts.
