You will need to wait 2 years from the closing date of your last Citi AA card before you are eligible to get another AA bonus with them.

Barclays does not currently have this same rule as far as I know. So you may be able to get another Aviator Red Card with them now.

I have not seen a direct link to get their Aviator Silver card. The only way I know to do so is to first get a Red card and then upgrade it to Silver if this is something you care to do.

Barclays issued the USMC, before it got converted to the AA Red Card. therefore I am confused with by your last comment, unless it was a really old card that was BofA (I think) from many years ago?