I'm happy to help you find probes for your MDO3014.You need probes for a spectrum analyzer, and I'm assuming that you are referring to the built-in Spectrum analyzer on the MDO3014 unit. If so, Tektronix actually has an FAQ that covers this question, linked below.
You also may be interested in the TPA-N-VPI Adapter. This adapter accepts probes with BNC, TekProbe™, and TekVPI™ connection interface. If you are currently using a probe with one of these interfaces, this adapter would allow the probe to be used with N connector of the MDO3000.
Links:
What probes are supported on the RF input of the MDO3000 and MDO4000 series?: https://www.tek.com/en/support/faqs/what-probes-are-supported-rf-input-mdo3000-and-mdo4000-series
TPA-N-VPI Probe Adapter: https://www.tek.com/en/manual/tpa-n-vpi
