Detailed data for IEEE 33 bus radial distribution system is given in the following reference
M. E. Baran and F. F. Wu, "Network reconfiguration in distribution systems for loss reduction and load balancing," in IEEE Transactions on Power Delivery, vol. 4, no. 2, pp. 1401-1407, April 1989. doi: 10.1109/61.25627
The values of source voltage and MVA from the above mentioned reference are 12.66 KV and 5084.26 kW for the base configuration. You can take any values of voltage and MVA as base values. May be you can start with 12.66 KV and 5084.26 kW as base values.
Simulink model for this system is discussed in the following reference
M. R. Kumar, S. Satyanarayana and V. Ganesh, "A simple Matlab/Simulink model of balanced radial distribution systems and its application to find optimal penetration of active, reactive and complex power to minimize power losses," 2016 International Conference on Signal Processing, Communication, Power and Embedded System (SCOPES), Paralakhemundi, 2016, pp. 924-929.