It may be worth condidering going to a copy shop. Things may have changed since I worked on Canon Colour Copiers but this is what used to happen. Using a Fresnel screen and projected light an image of the transpareny was projected on the the target glass of the copier and then copies made from that image. I seem to remember being able to copy up to A4 transparencies.
My Epson film and slide adapter on my scanner takes 4 mounted 35mm slides at once, with space to spare. I estimate that it's capacity is about 100mm x 150mm (I'm at work at the moment, so can't check). Would that fit your slides?
Note that misery suggested a professional photographer, not a photo lab as you seem to think.
Any pro photographer should be able to produce a contact print without specialist equipment (just specialist knowledge). From this you could scan and make as many prints as you want. A professional photogapher who is unable to do this should not be calling himself by that title.