I have contacted fgw customer services and they confirm that Swindon-Reading is eligible for a gold card, but this is not the opinion of all fgw ticket sales staff. Those at Swindon station will not issue an initial gold card, but will issue a replacement. To get the first one the ticket needs to be purchased from a 'network' station (rightly or wrongly). The thing is you can't argue with toc staff because they think they're right and if you carry on they will probably get the BTP▸ or private security thugs.
It used to be the case that all ticket offices carried gold card ticket stock. A few years ago it was decided that stations outside the network area no longer needed to do so. I dont know why it may have been to reduce the amount of ticket stock held. For example Glasgow Central would not sell many gold cards.
So stations outside the network area no longer issue the ticket on gold card stock but it is still a gold card. Best if you buy the ticket from Reading that way you can guarantee it will be gold card on gold card stock.
And the
TOC▸ staff at Swindon are correct so please dont argue with them.