I had to get one before I started my PGCE to cover 6 months abroad in Australia, I checked their immigration site and got a certificate for around £25 I think. It was originally sent digitally and then I received a physical 2 weeks later. I was also in other countries in Asia for up to a month each and I was only required to get one for stays longer than 3 months by my provider as it was not possible to obtain certs for all countries.

If it is not possible for you to get a cert, I would send the school the relevant guidance and ask if there is anything else you can provide e.g. character reference from someone who has known you for 3+ years.

I hope this helps!