Well, their FAQ says:
For different timezones, contact one of our qualified Proxmox resellers who will be able to offer you help with Proxmox solutions in your timezone and your local language.
Consulting the list of resellers that that page links to finds one that blatantly advertises 24x7 support, and it's likely that others will offer it if asked. See [0].Proxmox needs to better their reputation right now if they're going to be counted as a contender, and burying the fact that you can have 24/7 SLA is not a good way of improving that reputation of being mostly for the homebrew crowd.
No. It took me less than 60 seconds to find it.
> ...the lack of it front and center probably scares away a lot of clients.
I've done on-call enterprise support for the products that I and the folks I worked with maintained and extended. We were whatever tier "the folks who work on the product" is. [0]
I can pretty authoritatively tell you that the folks who are scared away by a 60->120 second search to answer the question "It looks like this one vendor doesn't offer 24/7 support, but they do offer a list of certified support vendors. Do one or more of the vendors they certify to provide support and training provide 24/7 support?" are the sort of folks you rather don't want as customers.
[0] Tier 2? Tier 3? Who knows?