Hello fbskethcher, welcome to Stamp Community!

The card would be similar to Canadian cards or USA cards. (country of Canada as opposed to country of Newfoundland at the time)
Nice info and scan, thank you. Proper place for it also.
In the Unitrade Catalogue of Canadian Stamps it would not be shown as it is a specialized type of event thing.
It would be shown I the Newfoundland specialized catalogue I would think, which unfortunately I do not have but has been mentioned on SCF here before.
The card and stamp set, if just sold as a stamp set, would be priced as used stamps as there would be no gum on them, so used no cancellation grading. Very fine stamps in grading otherwise though.
Similar to diplomatic presentation cards or portfolios gicen as gifts to visiting political dignitaries (high ranking in society persons, dignified)
Looks to be well designed and looks nice on first appearance, the eye appeal thing.
You would sell it to a specialized collector of Newfoundland or British Commonwealth countries, or of King George V coronation material, (or flags) stamps or otherwise.
It would make a great frontispiece for an album display or a stamp show or postcard perhaps? display.
Any wear and tear or corner nicks or cuts and scrapes would devalue it immediately, unless the pruchaser wished to cover the nicks up himself by borders or something.
For costing and valuation I would show the back also and mention and stains or cuts or etc on
ebay or to a buyer, if that is your choice. Good pictures under well lighted conditions (daylight is best) always sell an item. The actual cost or selling price would be maybe $20 I would wager, just from seeing material of the same era.
the market is always changing and Newfoundland material has been on an upswwing lately. Great addition to a collection I think.
Doug