How do you progress your familiar without taking more levels in that class?

Question

I am playing a cleric/wizard/Mystic Theurge. I choose the familiar class feature for my wizard. MT only progresses a wizards spell casting and caster level. You do not learn new spells and the familiar does not gain increased abilities according to the familiar chart.

Is there a way to improve the familiar according to the chart without taking levels in a class that grant a familiar? I mostly want the ability to speak with it at level 5, and the all important spell resistant at 11th (which gets better the higher level I am).

The Iron Will/Familiar Bond/Improved Familiar Bond is not the route I wish to go because it requires way too many feats and Im already feat starved.

I know of Boon Companion, but that increases the total by 4, which helps (more so once I can get SR).

Answer 1

1. Wasp Familiar:

This feat grants you a familiar using your character level as your level for it.

2. Skill Focus/Eldritch Heritage (Arcane Bloodline)

Detailed more closely in this answer, Eldritch Heritage (Arcane Bloodline) would increase the effective level of your familiar.

3. Iron Will/Familiar Bond/Improved Familiar Bond

I know you'd rather not go with this, but it is a way to get a familiar that progresses with your level.

Honorable Mention: Boon Companion

This feat does not give you a scaling familiar, however it does increases your familiars effective level by 4.