I think Beseler makes a variable contrast light source for medium format but not for the 23 models. I think it is for their 6x7 model enlargers.
In 4x5 they made a universal light source which is no longer available and difficult to find used. I use a Beseler 4x5 VXL enlarger with the Dichro 45S light source for variable contrast B&W printing.
Don't know about availability in Europe. However, given the huge markdown for buying used, you might do well buying a used model in the US and paying for shipping. You could easily buy a Beseler 45 MXT with a Dichro 45S light source on Ebay for $450. Shipping would be high but you would still be way ahead.