Can I use a calibration kit from another vendor with my Bird VNA or must I only use Bird calibration kit?

To answer this question, you need to take into account two calibration kit options: manual or electronic. 

Yes, you can use a manual calibration kit from another vendor to perform a measurement calibration on your Bird BNA100 or BNA1000 vector network analyzer. When you use the TVNA software menu bar to navigate to Calibration->Cal Kit, you will find a long list of popular cal kits to choose from.  

Should you prefer that your VNA and cal kit come from the same vendor, all manual calibration kit options from Bird are listed below: 

Note, too, that if you have a calibration kit that is not accounted for in the list, you can create up to two custom "User" cal kits, inputting the coefficient information for each standard from the documentation provided by the manufacturer of the cal standards: 

For electronic calibration (ECal) kits, the options are much more limited. Because the calibration and automatic port sensing routines have their execution built into the TVNA software, you will need to use one of the ECal kit options from Bird shown in the list below. 

For information on Bird VNAs, see https://birdrf.com/Products/Analyzers/VNA.