Get Optionset values dynamically from CRM to WordPress

How can we get Optionset values dynamically from CRM to WordPress ?

Currently we are hardcoding the option set field values with the name , but how can we make them dynamically.
Below is the code snippet we are using currently :-

<label for="av_reference">Referral Source</label>
<select name="ReferralSource" id="av_reference">
<option value="814760000">Facebook</option>
<option value="814760001">Twitter</option>
<option value="814760002">Instagram</option>
<option value="814760003">LinkedIn</option>
<option value="814760004">Newsletter</option>
<option value="814760005">Website</option>
</select>