I have been single for years just turned 30 etc.
In the last 3 years what I have done is flirt with female friends who already have boyfriends to see if they react since they feel comfortable with me and know I am not trying it on.
Each response has been positive to the point of "wow" even unintentionally had a few girls pretty much flirt back with me as they say their relationship is failing (not that I would encoruage cheating so don't)
Its been to the point even ones that don't know im single are shocked and trust me so much they give me their intimate life details and do things like snuggle up to me and get very affectionate as they tell me how great I am (so its not the we feel sorry for you sort of talk)
Not sure what to do about finding actual single women to date though, I may be good at flirting when I have no pressure i.e they are friends but useless at selling myself on paper (which is why I cant get a job without someone rewriting a statement for me but always pass an interview should I get that far) I had a few online dates before (out if hundreds of first messages I sent I had like 4 dates in 8 years from them all failed as I was nervous at the date)