The conjugation tables of irregular Latin verbs that I have seen do not give any imperative forms for the verb velle. The verb nolle has the imperative forms noli and nolite, and they are fairly common. I found no hits for the forms voli, volite and velite in a corpus search, and all hits for veli seem to be from the noun velum. Have the imperative forms of velle ever been used in Latin of any era? If yes, what are they?
There are some rare cases where one might want to use such imperatives. I heard a nice speech in Finnish in December, and it made use of similar imperatives at a key point. To get an idea of how the situation, consider the following fictive speech excerpt:
I could ask you to serve your country. But I will not. The most important thing is not that you always succeed or that you even try in every single situation, but that you always want to do the best for your country. Want to serve your country!
I am not asking how to work around the seemingly missing imperatives; that is covered in another question. I am asking whether they are really missing. Do ask for details if the question is not clear enough.