i used to buy my replacement pads in this store, you could have a look. http://www.6order.hk/epadstore

I personally tried this one instead.  I think they are better, and it's even cheaper.   http://6order.hk/epadstore/index.php?route=product/product&product_id=68

If so, perhaps, you need to pay attention to measure the inner hole of the new earpads.  the ear pads inner hole size from different brands can vary a lot.   you can try to check this site to see if their pads can fit you or not.   jntmall ear pads

Check your old ear pad size , and then find it here.   most of the them, it depends on size only.    replacement ear pads

I used to buy one from this store.  100mm ear pad, with cloth for covering driver unit already.    Seems it's a worth deal, as they are free shipping to US.  100mm jntmall ear pad

3.5in for AKG 145S   I also get one from this store. 3.5in ear pad   Hope it helps you guys.

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The original HD 598 ear pad should be hard to find, as they are in good quality polyurethane.   Trust you should measure your old ear pad size first before purchase.     The below link may also help you.   I used to buy from them before.   ...

I've tried their pads, quality is ok, but you have to wait.  Their shipping is just fair. I noted that they have a site-store now, you may have a look. http://www.jntmall.com/store/

luckily, i found such a site in Google.  collar headphone clipper,   http://www.jntworld.com/catalog/product_info.php?products_id=236   only 4USd for 5 clips already