The Shipyard Oder is not selling guns for the Rheinland Battlecruiser. You can only buy it at battleship Strausberg. Not sure if it's a bug but it's strange not to be able to buy the weapons from the place you bought the ship.
@"Erzie" Oder Shipyard, a Daumann base, is a shipyard which specializes in building and maintaining capitals (incl. their associated equipment, namely weapons) for RM/RFP/BDM. This unnecessary "change" breaks more than a few things in our current line of on-going RP. Please have these moved back to Oder.
From the information we gathered, we did not move anything. The battlecruiser weaponry was just not added to Oder. Additionally, system development and story development is not my department, so don't expect me to "adhere to lore" when items are added.
Upon further review, the guns are showing as being sold on Oder. Check your reputation. Sell locations were set to the same locations that cruiser turrets are already sold.
Check your reputation with Daumann, Oder shipyard is a daumann base and requires .89 rep with them to buy battlecruiser weaponry.
Sell locations include the following battleships: Altenburg, Bayern, Braunschweig, Karlsruhe, Koblenz, Schwerin, Stausberg.
And then Oder Shipyard.