Best Electronics is alive and well and in their 39th year ... I just got a bunch of parts from them. SIO port does not seem like an impossible thing to get. You might have to purchase the whole board, which for the price may be worth it vd the effort to decoder and resider a new port connector. Give them a try. best-electronics.com
The guy running it it a bit eccentric, but highly knowledgeable. I got my stuff in 2 days from California to New York. Great overall service. I just wish he would update the layout of his web site as it's in a state that was written in 1993 era web design and navigation is a nightmare. However, if you get a nice hot cup a coffee and some free time, you will find loads and loads of useful tips, tricks and trivia knowledge sprinkled all over the web site. Example - he goes into the CX40 joystick design, the various incarnations, does to the style of trees on the PCB nd the style contact dimples used .. like really really deep into nuances of just about everything. Yes Electronics also has gone out of their way to engineer and improve some of the Original Atari designs.... I'm impressed !