I had to replace small fluorescents in a bathroom vanity mirror last year, same sized tubes they were available, However there were out of tolerance just a fraction too long. I replaced the fittings to use the newer LED tubes. Not far off the same price.
I don't have the specifications of the tubes I bought, I took them back and got a refund but they were the thin tubes and unbranded. The OP could try CEF here in the UK or RS Components.
As fluorescents are being slowly withdrawn in the UK/EU it made more sense to install 2 LED strip lamps, it was a simple to do.
Have you ever thought of getting an LED light tablet? The great thing is that they last for over 30,000 hours, dimmable and stays cool. I've owned one for 5 years and I've never regretted it. Fluorescent tubes are known for UV transmission. LEDs might be better for your eyes in the long term.
I don't have the specifications of the tubes I bought, I took them back and got a refund but they were the thin tubes and unbranded. The OP could try CEF here in the UK or RS Components.
As fluorescents are being slowly withdrawn in the UK/EU it made more sense to install 2 LED strip lamps, it was a simple to do.