Hi Peter, if you are looking for somthing to add to a Pi for your own build whilst waiting for the PiSupply products to come back into stock (thought they had them at recent Things Conf! have you checked website/store or just waiting for the email? - and I believe Al and the team at ConnectedThings were selling PiSupply kit in the store at the show), alternates from e.g. iMST and RAK Wireless and several others look to be readily available in stock - manufacturers and disties. As alternates to TTIG (in stock at RS and elsewhere as above) then I can readily see iMST Lite GW in stock (Pi based), RAK have Micro GW, LoRa DIscovery Kits, Pilots (both again Pi based), and others in stock, Dragino and disties look to have LPS8 & LG308 (note full LoRaWAN GW’s not the naff LG01/LG02 single/dual channel packet forwarders masquarading as GW’s) in stock, several disties have Laird RG186 in stock, Several have Tektelic Kona Micro Lite GW’s (Not the more expensive Kone Micro GW) in stock, etc.
With respect I suspect you havent looked very hard 
Talking of Al and the ConnectedThings Store (@eggfriedrice), as noted they were running a store for nodes, GW’s and accessories as part of the show in Amsterdam and I know they brought a lot of the un-sold stock back home so if not delayed in transit I would suggest you give them a try…
If you step up a bit on price then Farnell still carry and hold stock of the original TTN Kickstarter GW, and several disties are holding stock of e.g. the Tektelic Kona Micro and Multitech AEP GW’s…
Happy Hunting!