how..? Search {n} char or {-n} using regex...?n}

Don't do it with a regex - they are text matching systems, not text processing. They don;t have any provision for converting substrings to numbers, so your regex would have to explicitly check for {1}, {2}, {3}, ... {999} which is ridiculous (and error prone).

Instead, do a Regex which finds the number - that's trivial - and then extract the substring after it in C# or VB. The Match object that the regex returns includes the Index and Length of the matched text, so extracting the substring after that is trivial in either language.