A couple quick searches on Ebay:
M35 emblem $4.99 US - without the X
http://www.ebay.com/itm/NEW-Infiniti-Ch ... 464wt_1152
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M35-S emblem. $25.95 US Just yank off the S and hold the template so your X sticks through and it will line up perfectly:
http://www.ebay.com/itm/NEW-OEM-INFINIT ... 1818wt_915
***** These come with the blue foam templates - simply hold the upper edge of the templates against the top of the trunk or against the top of your rear spoiler if you have one ... at the same time, line up the outer edge of the foam with the outer edge of the trunk lid.
As for removal of the existing badge, the idea above is a very good one. You can also pick up adhesive remover at any auto parts store - get a liquid if possible instead of a spray so oyu can soak the edge of a towek with it. I use a plastic squeegie to get under the edge of the letters and slowly work it all the way under to pry it up - no worries about it pulling the paint off - just wet the area and heat it with a hair dryer (NOT TOO HOT) and it comes off very easily. Then clean the surface with adhesive remover until you can no longer tell there was anything there.