Yes. At Rocket Dollar, we sell IRS pre-approved retirement plans for your Self-Directed Solo 401(k)
A pre-approved retirement plan is a plan sold to employers by a document provider such as a financial institution or benefits practitioner. The document provider is the “pre-approved plan provider.” The document provider requests IRS approval (“pre-approval”) of a defined contribution or defined benefit plan document as meeting the requirements of Internal Revenue Code Sections 401, 403(a), or 403(b). The pre-approved plan provider then makes the IRS-approved plan available to adopting employers. The IRS also issues opinion letters for prototype IRAs.
* From the IRS website on pre-approved plans.