For BCrypt implemented in C#, please see:
BCrypt.Net.
Perhaps your Web search problem was looking for "implementing bcrypt into C# desktop applications". How the concept of "desktop" or anything which is "not desktop" could be related to the topic? The search string could be just "BCrypt C#". Maybe all you need is to embrace
separation of concerns. :-)
And for password-based authentication, I would recommend using SHA-2 (or SHA-3). It's the matter of using it correctly. Shooting from the heaps, your argument that SHA algorithms are too fast and hence allow the malicious artist to "calculate a lot of hashes" just doesn't look serious. Let's say, the legitimate user goes through the authentication cycle only once, so a little slower calculation of the hash does not matter. But you can always slow down this cycle on the server part. I don't say that this would make a viable security technique; I just mean that this consideration breaks your speculations on the benefit of other algorithms based on speed. Generally, the whole idea of security of some algorithm based on its slow speed sounds absurd. It has nothing to do with real security features, such as lack of
backdoor and
cryptographic feasibility of brute-force attack. See also
https://en.wikipedia.org/wiki/Hash_function_security_summary[
^].
—SA