Any markings on the lock? Might have to pick it open or have a locksmith do it for you unless you want to try and drill it out.
A locksmith can pick it with a decoding pick and then cut you a key to replace the lost ones. I guess it depends on if you want to retain the ability to lock it.
This is where I buy my lock pick sets but you need to be aware of local laws regarding buying and possession of them.
http://www.lockpicktools.com/tubular-lock-picks/
Here in MN it is illegal to have them if you are committing a crime. If you just have them in a bag or in your car there is nothing wrong. In other states, simple possession is a crime unless you are a licensed locksmith as they consider them burglary tools.
Another route might be to look at some youtube videos on opening a tubular lock with everyday items such as a Bic Pen body or McDonalds straw. Many people assume tubular locks are more secure because the key is round but this isn't the case.
Oh and the only Master Locks I own are ones used to keep up on the skill of picking. Though they are not much of a challenge, I can open most faster with a pick set than fumbling for the key and I am not a locksmith. I do work in the security field and physical security assessments are part of what I do.
