Do your calibration kits come with a certificate of calibration.

Yes. All Kirkby Microwave VNA calibration and verifications kits include a calibration certificate, which includes:

Calibration certificate number.
Name of customer
Date of calibration
Model number of kit
Serial number of kit.
Any special options, such as an extended frequency range.
The place of calibration - currently Kirkby Microwaves office, in Chelmsford, UK.
Date when the next calibration is due - this is 1 year after the initial calibration.

In addition, there's a sticker on the front which includes some, but not all the information from the calibration certificate. The sticker has

Calibration certificate number.
Date of calibration
Date when calibration is due
Serial number of kit.

Here's a sample calibration certificate.

Getting a Kirkby Microwave VNA calibration kit recalibrated.

The cost of getting a Kirkby Microwave vector network analyzer kit recalibrated is £100 plus carriage. Please contact us prior to sending a kit for calibration. There are some issues with customs duties for kits sent from outside the European Union, so please contact us by email or telephone to discuss this.

When a kit is sent for calibration you will receive

A quick email acknowledging receipt of the calibration kit, as soon as it is received, and before any tests are performed.
After a the kit is tested, you will receive a brief email stating whether the kit has passed calibration, or whether any of the components are out of specification and so need replacing. If replacement parts are needed, the cost will be quoted.
The S-parameters of each calibration standard, as well as revised coefficients for the standards.
A new calibration certificate.
A new calibration sticker, showing the date calibrated, when the next calibration is due, and the serial number of the kit.
A tracking number sent as soon as the courier is booked to collect the kit.

Kirkby Microwave Ltd is registered in England and Wales, company number 08914892. Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT.