Any probes that have an interval of compensation, so that the input capacitance of the scope (which is 20pF) fits somewhere within the interval of adjustment are ok... You can buy them on ebay... The original Tektronix probes are too expensive in my opinion and there are many alternatives to that...
About the bandwidth, the quoted bandwidth is given at -3dB (
http://www.ens-lyon.fr/DSM/AGREG-Physique/oral/Notices/N036-003.pdf) to be (at least) 100 Mhz from 5mV to 5V/div and 90 Mhz at 2 mV/div... And it also deacreses by 10 Mhz when the ambient temperature rises above 35 degrees celsius...
The bandwidth of the probes is also given at -3dB... So, in my opinion, you don't earn anything by buying an 150 Mhz probe...
It is very rellevant what you intend to do with the scope... If you want to just check the presence or absence of a signal (and the wave shape does not matter much at all), of course you can use this scope well above 100 Mhz... But the signals (any other than sinewaves) will be distorted... And there will come a point where the harmonics are attenuated so much, that you only see the fundamental... And you would see a 150 Mhz sinewave, which in reality might be a squarewave... And it will be confusing...
If you only want to measure sinusoidal signals (which I doubt), you would only see an attenuation at frequencies above 70 Mhz or so (where there is no attenuation at all - 0 dB)...