Just pay it forward......;-)
There are several types of yellows used in medieval painting. Where as gold leafing may be used for parade or funerary crests or for high ceremonial uses there are plenty of substitutes used medievally that can make things "gold like".
To, the heraldic blazon of "or" represents gold in all its forms. It does not distinguish between metalic gold or yellow, nor does it specify the tone or hue of yellow (or gold).
Yellow ochre is an earth pigment and varies from bright yellow to olive. Its mixed with mediums to make stains to opaque colors.
Orpiment is a bright yellow and comes from auripigmentum, (the color of gold). Derived from a sulphide of arsenic found in nature as a stone. It so resembled gold that alchemists tried to extract gold from it. Orpiment was a pretty regular component of medieval painters ti imitate gold and in its natural state has a metallic flake to it. Orpiment did have problems with being mixed with certain other paints and could cause problems. Colors like verdigris or lead white would cause a reaction and the paint would fail or corrode. Sometime causing decay of the surface it was painted on from the reaction.
Bile yellows were a substitute for orpiment and were made from fish gall or bile, calcium, vinegar and chalk.
Giallorino/Massicot is another earth pigment and may have been derived from the earth pigment and lead and antimony. Its described in medeival texts as a "very attractive yellow" . This was used to lighten other colors without turning them pastel. i.e. added to green or red much like we use yellow to make highlights of green without truning it sagey or to tred to make a warm highlight rather than pink.
Another cheat was to laquer white metals to make them look gold. Putting a yellow stained laquer over tin and silver to give a gold look. (so it seems the technique of painting tamiya clear yellow over brightened metal on figures is nothing new).
Mosaic gold is a sulphide of tin and was used from the 13thc. on in western europe. It was used as an illuminator's gold and was a substitute for gold leafing in manuscripts and on some panel painting. It would look like a bronze powder and was mixed with a medium to paint.
Celandine was mercury mixed with egg yolk and stained yellow with celandine to give it a gold metallic sheen.
There were also several stains and paints made with aloes, caballines and hepatics. This over tins and silver had a nice gold effect.
Saffron was also used to produce yellows. Also Buckthorn, weld and fustic.
So you can see there are plenty of yellows to paint your crests and shields with. And they can range the gambit from metallic to yellow to achieve the results.