At the consecration of a church wax/mastic is being used to seal in the relics into the Holy Table. Also the table top of the Holy Table is secured with wax/mastic and nails. Small reliquaries with relics are also have often the fragments of relics encased in wax/mastic to secure them.
The process to create wax/mastic is generally described in the order of the Great Consecration of the Church. However it seems that the ingredient list is also depending on local traditions.
The common ingredients of wax/mastic are:
-Gum Benzoin Sumatra
-Gum Olibanum (Frankincense)
-Pure Bees Wax
Especially the resins (gums) and marble should be in powdered form. If they cannot be obtained in powdered form there should be ground before usage. An electric coffee grinder will help with this process.
Example suppliers for the ingredients
Some items on the ingredient list can be challenging to procure. Here are some example vendors for those items Gum Mastic:  Gum Benzoin / Gum Myrrh:   Ground Marble  Gum Olibanum / Rose Incense / Rose Oil: any Orthodox incense provider has those for example