Depending on the model, Case/IH probably still has them. And sometimes they are really close, and strange sometimes, less than aftermarket parts.
What model is your tractor..?? You can go to Messicks, and use the online parts feature at the top left of the page in the menu. Place your cursor on the "Online Parts", then select Case/IH when it appears. Enter you model number in the block, then select your model out of the list that appears next. Then select the component they would be in,and click on it. An exploded view of selected component, list of parts by description, and price of part will appear.
If you want to compare OEM prices against aftermarket parts, copy and paste the part number to a search engine, such as Google, and you should get a ton of hits.