I’m so sorry to hear that! I just came back from a camping trip and family visit in the North Country, and my daughter was telling me they were putting off projects for a year or so for the same reason. I know you don’t want to do that with your oven project.
I am looking again at the masonry supply store locator, and it looks like most of the masonry supply dealers in your area are marketing complete kits. In my own build, I used Harbison-Walker’s “KS4” mortar, which meets all the specs and sells for about $55 for a 55 lb bag. (It may have gone up in the past few months, but the last purchase I made was last summer.) I needed 9 bags to complete my oven, but it was totally worth it for the convenience.
FireRock looks pretty pricey, and you’d use roughly the same amounts as I did. It appears to come in 25 pound bags, priced at an eye-popping $204 a bag in one online outlet (and that was a “sale” price!)—but I also saw an outlet in Georgia that would sell it for $40 a bag out the door. A product specialist at one outlet admitted that it was “similar” to heat resistant mortar but was designed for FireRock products only.
My suggestion would be to bite the bullet and call the HWI outlet in Cheektowaga. If you own or have access to a pickup truck they will palletize your order and load it for you. Company-wide, they are supposed to be aware of BrickWood specs and should be recommending this or a similar product—but you can save the trouble by just asking for “KS4” and explaining it is for a BrickWood pizza oven.
Hope this all helps, and please let me know how it works out for you.