In this question I discussed how sharding a private key with Shamir's Secret Sharing Scheme maybe a good alternative to MultiSig as a means of reducing excessive fees associated with MultiSig transactions. @Pieter Wuille provided an excellent analysis of the pros and cons of using Sharding vs. MultiSig and revealed some of the work in progress aiming to address the main concern with sharding (the "A Chain Only as Strong as Its Weakest Link" problem).
As mentioned, the main problem with employing SSS as an alternative to MultiSig is that it is necessary to reconstruct the actual secret key on a single machine before signing a transaction - once again making it vulnerable to a single point of failure (attack). As the saying goes "a chain is only as strong as its weakest link".
While Taproot and Schnorr signatures were proposed as potential alternatives to SSS, these two solutions are for the time being just "proposals" and they will need to be accepted by the entire Bitcoin community (which could take forever) before they become viable alternatives.
Are there any alternatives to SSS, which can be used right now, where a transaction can be signed by two (or more) parties without needing the secret key to convene on one machine? Are there any alternatives to "Shamir's Secret Sharing" that might allow this functionality?
In case it makes a difference, all I need is n-of-n (i.e, 3-out-of-3) rather than k-of-n (i.e, 3-out-of-4 or 2-out-of-3).