OPA129UB; 2156-OPA129UB-ND is an obsolete low input bias OP-Amp made by texas instruments. I used the following specs to find a cross with similar low input bias:
| Specification Name | Value |
|---|---|
| Ampifier Type | General Purpose |
| Voltage Supply | 10-36V, +/-5-18V |
| Package/Case | 8-SOIC (.154", 3.9mm Width) |
| Current - Input Bias | 0.03pA |
The closest item I could find was part number LMC6061AIMX/NOPB; Digi-Key part number LMC6061AIMX/NOPBCT-ND. While the input voltage is different, you could still technically work with 10 to 15.15V single side source or +/- 5 to 7.75 dual side source. Sometimes you have to compromise with certain values to find something similar. The input bias is .01pA which is still pretty small.
Here is a list of other potential crosses: https://www.digikey.com/short/47fn7c just in case.
Please review the datasheets to ensure the alternative will work for your application.