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You can't really drop in any woofer into your cabinet. Specs matter. I don't see many affordable 8 inch woofers in India. Probably Bolton ( extinct ?), or Iwai or Dainty ( car speakers). Other brand woofers ( or sub-woofers ?) are available on Amazon.in .
What's wrong with your current Philips woofer ? Maybe you can fix it ?
Look at the offerings at diyaudiocart.com and diyaudioparts.com.
Always try to measure the T/S parameters of your driver. Usually expensive drivers are close to published specs but less expensive drivers can be all over the place.