Вы можете сделать это, используя querySelectorAll
let ele = document.querySelectorAll('select[name^=visitors]')
console.log(ele)
<select name="visitors10">
<option class="disableDuration4" value="5">5</option>
<option class="disableDuration5" value="6">6</option>
<option class="disableDuration6" value="7">7</option>
</select>
<select name="visitors11">
<option class="disableDuration4" value="5">5</option>
<option class="disableDuration5" value="6">6</option>
<option class="disableDuration6" value="7">7</option>
</select>
<select name="visitors12">
<option class="disableDuration4" value="5">5</option>
<option class="disableDuration5" value="6">6</option>
<option class="disableDuration6" value="7">7</option>
</select>
<select name="xyz"></select>
<select name="visitorsxyz"></select>