hi there Vic
Do you have access to basic tools? such as a 4mm die and a 4mm plug tap and appropriate drill which is about 3.5mm. If you do, the item you are after is quite easily made. I have done, and use this type of extension for the turrets on HMS Exeter. I very carefully drilled out the top of the servo where the securing screw goes in; but not all the way through - only about 5mm deep and then tap the hole out with a 4mm tap. I then found some 4mm brass rod and carefully put a 4mm thread on the end of that with a die nut about 10mm long. Then cut the brass rod to the desired length which I required and put a thread on the opposite end. I put a lock nut on the end that was going onto the end of the servo then and with a bit of Superglue onto the thread that is going into the servo - I screwed the brass rod into the servo and locked it down with the lock nut.
Then, if you require, you could cut a spacer tube to fit between the two lock nuts on the brass rod.
I do hope this is of some help.
I have attached a scribble to help.
aye
John