Sourcing Transformer with Specific Turns Ratio
Transformers are difficult to source in general. My recommendation based on past experience designing low volume one-off flyback transformers is to build your design around the transformer, not vice-versa. Coilcraft is an example of a company that sources stock transformers suitable for flyback applications.
I'm providing this as general advice for people designing transformer-based circuits. DO NOT use this design, or one like it, on a human being. High voltage converters are not toys and should be taken seriously.