You can buy a new cooler.
However, if you are going to buy a new PC soon, then perhaps spending money on a new cooler is not necessarily the best thing to do. You can buy the following replacement cooler for $12 + $2 shipping which is compatible with your card; at least according to the manufacturer's website. http://www.newegg.com/Product/Product.aspx?Item=N82E16835192006
An alternative is to buy a new card if you don't mind dealing with a mail-in rebate. The following GeForce 8400GS should be slightly faster than your 7300GT and can be purchased for $5 (after rebate and promo code VGAZ161A) + $4 shipping.http://www.newegg.com/Product/Product.aspx?Item=N82E16814500161