No, there isn't anything with a higher DXM content than 60mg per pill, not even in liquid form. By the way, it's not really okay to take the high amounts of guafenesin that's in Mucinex DM.
A lot of people abuse Coricidin Cough & Cold because they have more DXM than cough gels, 30mg. Please do not take these in high doses (over 6 pills which is the daily limit) as it contains an anti-histamine known to cause fatality when taken in high doses. Chlorpheniramine Maleate.
You can easily use a Google search and find out what cough syrups have the highest DXM content overall. Make sure it is the only ingredient. If you do not like syrup, there are a variety of brand and off-brand cough gels with 15mg of DXM each.
Use a search engine.