It is hard to recommend without fully knowing what type of RTDs you want to calibrate, your accuracy requirements, connections, etc. Do you want them to calculate ITS-90/CVD coefficients in instrument? The black stack was great because the binding posts are right there on top and easy to connect to anything.
If you want to stick to Fluke, email temperaturesupport@flukecal.com and tell them exactly what you need. Shane or Emmanuel are very experienced engineers who can recommend you a product or answer questions.
Otherwise, you could also look at a readout + iPad/PC software to calculate the coefficients.