You could use an InDesign GREP style for this:
1. Create a character style like "RefArabicNumerals" or "RefWesternNumerals" with e.g. Charis SIL.
2. Open the settings for the paragraph style "r" and navigate to GREP styles.
3. When you click to add a new GREP style, the example Regex should be the one, you are looking for: "\d+" (i.e. "one or more digits").
4. For applied format you choose your "RefArabicNumerals"/"RefWesternNumerals" character style.