I would recommend to look at the catalog at
www.minicircuits. com. They offer many mixers covering your band of interest. According to the frequency specification you can select a minimum number of mixers for your wide band. You will then have to carefully design the local oscillators which will need to be switched for each mixer. Do not attempt to run all LOs, the mixer products would be not controllable.
Mixers need to be accompanied with filters, at RF input to define the RF input bands, at IF output to obtain only the wanted products.
As an example, try to find schematics of old-style communication receivers. Typical commercial receivers cover 10 kHz to 100 kHz, 100 kHz to 30 MHz, 30 to 500 MHz, etc. An easier solution is to use the 0.1 to 30 MHz as the basic module and add converters to cover the lower and higher bands. Or try to follow spectrum-analyzer design, with switched RF bands and a narrower receiver at ~110 MHz.