You are looking for the wrong part number.
The part number you want is: IDS-TX-INT= (10/100/1000Base-TX for IDS 4235, 4250)
And it is still being sold by Cisco (List price $300).
It is only the base chassis IDS-4250-TX-K9 part number that has been End Of Saled in May.
The optional 10/100/1000 PCI NIC IDS-TX-INT= is still being sold for customers to upgrade their IDS-4250-TX sensors. The primary purpose for selling the additional NIC is to support InLine mode on the IDS-4250-TX sensors.
The IDS-TX-INT= can also be used in a IDS-4235 chassis for customers wanting to run InLine mode on their IDS-4235.
Because it can be used in both the IDS-4235 and IDS-4250-TX it was decided to not put 4235 or 4250 in the product number.
NOTE: IDS-4250-TX-INT is not a valid part number.