I think the shop that sells the pandora would be a good first idea. I'm not sure how the spare parts are handled now, but there is an email contact for non-standard orders on the actual preorder page. If you are sure you want buy them you could place your email to info@openpandora.de written like an official order with all the required information as noted on www.openpandora.org -> "preorder NOW" on the upper navigation bar. Please be patient then, depending on the workload of the (one-man) team it could take days until you'll receive an answer with your order details.
By the way, i don't understand why the tabs broke, could you please explain this? The usual use case doesn't require frequently battery removal? Or are they that tight that they require much force?