As far as having a local gold smith making a guard, I am sure it will be a lot more expensive than going through the "official jeweler" of LXA!
If you go to IHQ site or Herrf-Jones you can see the price of guards.
Of course depending on what you are purchasing will be the cost. I am not sure if they make it in White Gold anymore and needs to be a special order. What is funny, there is less gold in the white as will be only 10% but costs more!
As far as wearing Your Fathers Badge, if there was no guard with it, you can wear with your own Zeta Guard.
I am not sure if you bought Your Fathers own guard and add yours would be workable?
Checdk with IHQ and see they can tell you!
I know I was told I could wear my local Pin as a guard, but with LX Z, I really like to wear that as it messes with Brothers minds!

Both are important to me so I also put on the Local pin below and to the left of my LXA Badge and guard!