We'd probably need more background to help you, eg, are you currently a student? In what country? Assuming you're in the US, there are still some interesting things the Fed does wrt to payments, eg Fedwire, but getting into anything public-sector-related will be difficult at the moment. You could check out DCI at MIT Media Lab [0], they have some interesting projects in this space (eg Hamilton). If you're in a different country, most central banks are currently looking at CBDCs in some way. Many central banks also employ nationals of other countries, so you can cast a wider net than looking at just one country. In the private sector, there are several companies and/or academic groups that have helped smaller central banks set up their own CBDCs already, eg Cambodia uses Hyperledger with the help of some Japanese groups [1]. Word is that Polygon is also active in that space, but I don't have any references otomh. Larger countries will do a lot of development in-house. They will likely get outside help from the likes of Accenture or IBM. These could be good destinations themselves, but only if you're happy to be be working on something else most likely.

[0] https://dci.mit.edu/ [1] https://onlinelibrary.wiley.com/doi/10.1111/aepr.12464