OPA454 can be powered from 100V. There may be others. However, if you want 300mA then it is a power supply problem, not an amplifier. The simplest way would probably be with discrete transistors. Another option would be a high voltage opamp with external transistor(s) to boost the current capability. There are some opamps that will provide significant current such as the OPA547 which can do 500mA but only at 60V, not 100V. There may be one that does what you want - have a search of the various manufacturers.
Keith.