I can't even get the second battery I ordered at the same time as the camera.
As these have been with USA retailers for about 2 weeks, and the EU gets a similar number of Z9 bodies to USA - they
should be available in the EU - though as yet nothing in the UK.
Nikon UK have no idea when they can supply.
ASK YOUR RETAILER!
Nikon UK plays no part in distribution in the European Union and probably does not have the information you seek - though your retailer does.
Your retailer has access to a Nikon web-site which shows all their pre-orders, deliveries etc.
When a batch arrives in the Netherlands they are allocated by Nikon in the Netherlands to retailers. They possibly have to clear EU customs before they can be shipped to EU retailers. This part of the shipment process takes about 7 days.
Items for UK retailers have to to clear UK Customs for VAT (with a VAT refund to the EU). This takes around another 5-8 working days.
Your retailer can easily tell you if any batteries have been allocated to them (step 1) and if they have been shipped (step 2).
Nikon UK possibly/probably do not have access to this information - as they are not involved in product distribution.
As the batteries are available in USA there seems no legitimate reason why they should not be available in the EU, and on the way to at least some UK Nikon retailers.
When it comes to new product delivery many UK retailers inflate their initial order in the hope of getting a bigger slice of early supplies.
They came unstuck with the FTZ II as Nikon delivered masses of them several weeks ago - and hardly any Z 9.
My usual retailer in Harrogate has apparently had a second 105 S within 3 months of initial release - better than nothing - but not many as I know of others on their pre-order list.
Amazon UK seems to have bought a batch of 14-24 S from Nikon - and seem to be having trouble selling them at 20% below the usual UK street price - possibly because many Nikon users want a Z9 and second battery first - and cannot get them.
Slightly off topic Amazon UK have the 14-24 (mine was an official import) for under £2,000 - and they have been on offer for over 2 weeks.
Buying tactically the Amazon price varies between £1976 and £2086 - sometimes being cheapest before 7am in the morning.
You have to have a credit card set up with Amazon with sufficient credit - and you do not get a delivery time until shortly before arrival. You also need to be home during the day as Amazon email a security number shortly before delivery which has to be given verbally to the delivery driver.