Is it permissible to take a bicycle frame and its wheel to sell them, given that they have been there for months and their owner is unknown?

If the owner of the frame is known, it is not permissible to take it except with his permission. However, if the owner is unknown and the frame is exposed to loss, it falls under the ruling of a found item (luqatah); meaning it is not permissible to take it except with the intention of publicizing it for one year. It is also not permissible to dispose of it before the end of this period, while guaranteeing it to its owner should he come to claim it.