I don’t have any advice on where you might find a suitable co-founder with the skills/experience you (think you) are looking for, but as a software developer, I do have some thoughts on what I would recommend you to focus on when trying to find such a person.
You should look for a (good) developer who shares your excitement and passion for the product, who is motivated to work on your business and has the ability to learn your business domain as well as new technolgies and frameworks (if they are not already known) and not focus on people with (only) experience in specific programming langauges or frameworks.
Some things to keep in mind:
A skilled/experienced developer will be able to learn pretty much any technology stack or programming language in a reasonable amount of time. The time spent learning and understanding your business, product, problem domain and customer needs will most likely be much greater than any initial ramp-up time to learn a new technology stack.
In my experience, what makes a good developer a good developer is not so much related to what programming language or technology stack they prefer to use in a given situation, but rather how they approach problem-solving, their ability to learn and understand (new) problem domains and their general understanding of programming and design principles, best practices and patterns, and overall experience. The fundamentals of (good) programming and (good) software are pretty much the same across all technolgies.
The technology you think you need may not be what you actually need. Knowing the technology you think you need should probably not be a criteria for selcting a co-founder. Chances are your product can be implemented on several different technologies, and a technical co-founder should be able to help you make the technical choices for implementing your product. I do not know the background for your technical choices at this point, and I am not assuming that your choices are wrong, I’m just saying that a suitable technical co-founder should be able to tell you if your proposed technology is a good fit for your product, if another technology may be a better fit and to which extend the choice of technology is even relevant.
As with product development, the problem should come before the solution. Technology should be chosen only after one has decided on exactly what problem to solve and how to solve it. Chosing technology first may lead to a less than optimal solution, both from a technical perspective and a user perspective. A technical co-founder should be a person who is competent in helping you make that choice, after the problem solution has been found. The person shuld also be capable (and willing) to re-evaluate any previous technical choices as the product and business evolves.
Even if you already have (parts of) the product implemented with a given technology, I do not think you should limit yuorself to only considering people who have experience with that technology. A co-founder relationship will hopefully last a long time, while technologies tend to change rather quickly. The technical requirements may also change over time as your product and business evolves and grows. It’s therefore more important that the person understands the business aspects and shares your vision for the product than that they have specific experience with a given framework or technolgy at the point in time when the partnership forms.
If you find a person who shares your passion for your product or product idea and has the technical skills and knowledge to realise that product in software, you should focus on that rather than what technology that person may choose for implementing the product. Unless you (or the co-founder) make some really bad choices, the technology should not be of major relevance to the success of your product or business. Unless your product is really technical in nature (most software is not), your users will not care about the technology used to implement it. They will care about the value the product provides to them and the user experience they have when using it.
Note: I am somewhat assuming that you are able to find a good developer to be your co-founder. If you are not able to find a good developer, you are possibly better of by picking someone who already knows the technologies you are using (or planning to use).