Did you still need such converter?
I suggest look on HOLT website (see: http://www.holtic.com/category/352-arinc-429.aspx
You can use quite new and really good HI-3593 with SPI interface from ARINC side.
For RS232 there are a lot RS232/RS422/RS495 transceivers on the market, so use what you want.
The most difficult think is the "heart" of any converter.
You need to make not only physical convertion between interfaces which are electrically different but you need protocol convertion.
It could be done only by microcontroller in between ARINC IC and RS232 IC.
If you need only electrical conversion between ARINC and RS232.
It is another story and it looks much simple.
If you still interesting in, I will try to suggest you some solution next wee.
Just now I also work on such simple hardware converter to allow communicate with ARINC devices via standard COM.
I expect first results mid April.