Do I have a legal right to take back goods that have not been paid for

Absolutely not.  Your dispute is with the broker, not the end user.  You may be able to place a lien on the machine parts, which could be valid up to the amount that the end user owes the broker, if anything, but certainly not to reposess them.  Even if the broker still had the parts, resorting to "self help", in the form of taking property from someone else without any court order or oversight, is fraught with danger, both physical and legal.  Most courts frown  upon it, especially if there is a risk of a breach of the peace when you try to take the property.  If you think the end user could pressure the broker into paying you, you may want to considersimply writing a letter, or starting a lawsuit and seeking discovery from the end user.